This site must be the most civilized and knowledgeable group of car people on the internet, I do appreciate the experience and thoughtful responses from the experts here.
Here is some general information for future people who might be searching this out. I've searched out quite a bit of this and figured I would compile some notes here.
Calculating Fuel "Mass Flow Rate" Requirements for Engine
Step 1: Assume a Brake Specific Fuel Consumption (BSFC) Value
This is based on your engine's fuel efficiency, it is the amount of fuel the engine will consume to make 1 HP. Unless you have specific test data, it will be necessary to make an assumption here based on an approximate range typically between 0.5 and 0.6 pounds of fuel per horsepower-hour [ lb / (hp*hr) ].
Step 2: Calculate Mass Flow Rate for Fuel at Peak Horsepower based on BSFC
Mass Flow Rate of Fuel = Peak Horsepower * BSFC
For a general example, assume 700 HP peak and BSFC = 0.6. The mass flow rate of fuel would be equal to 700*0.6=420 lbs/hr.
Step 3: Convert Mass Flow Rate (lbs/hr) into Volume (Gallons/Hour) Based on the Density of Fuel
Assume a ballpark density for gasoline of 6.07 pounds per gallon.
GPH = Fuel Mass Flow Rate / Fuel Density
GPH = 420 / 6.07 = 69.2 GPH
Step 4: Add a Factor of Safety to the GPH
The factory of safety is based on personal preference, but you would ideally want a pump with some extra head room. For example, in the case of a system plumbed with a return line you would ideally want the pump to supply enough flow rate to the engine at peak power while also keeping the return line full.
Let's assume a factory of safety equal to 1.2 here.
GPH = GPH * 1.2 = 69.2 * 1.2 = 83 GPH
With this information you can start shopping for pumps.
Step 5: Not All Pumps are Created Equal
This is where things get confusing and the information at various websites is conflicting or incomplete. The most important aspects here are the pump's ability to handle "dry lift", the "pump pressure and volume curve", and "current draw".
Pump Curves
Each pump will have its own curve dictating what volume it can supply at a given pressure. This is a lot like an engine dyno run, any given fuel pump will only be able to supply a certain amount of flow volume at a given pressure rating. Typically a Holley carburetor wants 7 psi at idle and at least 4 psi at wide open throttle. The pump makers will let the marketing department fudge this all up, and advertise the highest flow rate even if it is nonsensical in practice. If possible, try to track down the actual pump curve or select something with lots of extra margin based on the numbers they provide. Don't just assume a pump rated for XYZ gallons per hour will run your XYZ gallons per hour engine at the desired fuel pressure. Trust by verify as Regan said.
Dry Lift Suction
Dry lift is also important, because the pump might need to handle a little dry suction in order to get the fluid flowing from the tank. This is where all the internet bench racers keep repeating the phrase, "mount the pump close to the tank and near the bottom of the fluid level". It is generally good advice, but it isn't the final answer. When building a car, you know there is a constant battle to package everything and never enough room where you want to mount stuff. Some pumps suck, they don't mind pulling fuel up a vertical lift. You might have a case where the pump is near the bottom of the tank, but it has to suck the fuel over a bump to establish a siphon effect before it will start flowing. For a particular application, you might need to mount the pump above the tank a bit. Lots of pumps can handle a decent dry lift height if you're shopping for that. Lots of pumps might advertise themselves as "self priming" to let the end user know they can handle a dry start by providing some suction to get things going.
Current Draw
Current draw is also an important parameter, the Ford 1G alternator used on FE engines isn't very impressive. Lots of people will convert over to a 3G alternator or use a high output 1-wire "1G" alternator to make more juice. All these current draw sources add up. You might not notice it right away, because the battery is acting like a giant electrical buffer. The battery is masking the low output from the alternator by covering for the deficit. Lots of guys put their weekend car on a battery tender in-between drives. If you do a bunch of short around town trips, and keep the battery topped off with a 110v wall plug in device, then a corner case might arise on a longer road trip because the battery buffer runs dry and the alternator isn't keeping up over the long run. Keep an eye on the total electrical demands.
Check Valves and Pull Through
Various pumps will also include check valves and shut off mechanisms. The check valves prevent back flow of fuel from the pump to the tank when the pump is off. This is useful for keeping the pump primed with fuel. It can also help with dry lift abilities, so the pump isn't working against gravity if it is providing suction in a "pulsing" mode. Another pump feature is a shut off valve, some pumps are equipped with the ability to shut off all fuel flow through them when the pump is not running. In this case, you can't "pull through" the pump with another pump. Imagine an electrical pump feeding mechanical pump. If you want to prime the fuel system with the electrical pump, then shut it off and run the car from the mechanical pump, you'll need to select an electric pump with the ability to pull fuel through it while it is de-energized.
Parallel and Series Pumping
Pumps can be staged in parallel to provide more mass flow rate, or in series to accomplish a pressure boost. It really depends on the specific application and pump, but these types of layout are all possible. Perhaps you have one pump feeding a swirl pot from the main tank, and a second pump pulling fuel from the swirl pot to the engine. Maybe you need two smaller electrical pumps in parallel to provide the mass flow rate needed to supply the engine.
Electric Pump Controllers
You can use a simple toggle switch or a logic device to power the pump. In more extreme cases, you might have a pump run by PWM (pulse width modulation) which sends 12V power in pulses to the pump in order to control its flow rate. A simple pump controller is sold by Revolution Electronics under the 12003 part number. It is on Amazon and eBay. This controller will turn the electric pump on for 3 seconds to prime the system with key on. It also has an input from the tach to shut the pump down if the engine turns off. The controller can trigger a relay for high current pumps, or directly control a lower current pump. In some cases, folks use an oil pressure switch to shut the electric pump off if the engine cuts out. This is a useful safety measure, you don't want the pump running full tilt in an emergency situation.
Electric Pump Mechanical Design
From what I have found, there are three common types of mechanical designs used with electric powered pumps. These are
1. Rotary Vane
2. Gerotor
3. Solenoid Powered Plunger Pumps
Each of these pumps has different characteristics which might make it more desirable for one application or another.
Traditional Mechanical Pumps
These generally run out of pumping capacity for high HP engines. Things start to get suspect for mechanical pumps when you're making over 450HP or so. Over time there have been a number of high performance mechanical pumps which have come and gone. The FE engine has a hard time accommodating a big mechanical pump without some grinding, which is no fun on your fancy high dollar new pump. RobbMc seems to be the best source of high HP mechanical pumps these days, but expect to do some grinding.
Other Pumps
If you're running methanol or E85 with a high HP engine, the mass flow rate might require a belt driven pump. These are a bit more exotic and expensive, something like two spur gears running off a belt to pump large volumes.
