A partial Vin? That can be traced back to the line and model.
What's the rest of the engine? Heads, intake, dizzy, carb, damper, these are clues as to the quality of the build.
If it's a quality build and you like the car then I would not be so fixed on the 28. jmo

Actually that is a big issue as you wouldn't want to pay for a 428, and get a 390, or worse a 352, that someone dumped in the vehicle to make it look correct.

My take on that is that you can never have too much flow from the water pump.  The thermostat will function to restrict water flow to the radiator, but I'm not sure that enters into the equation.  Not to open up a somewhat famous argument about cooling  , but I'm not one of those folks who believes that you need to slow down the water in the radiator to make it cool.  No matter how fast the water is going in the radiator, the same amount of water is contained in the radiator at all times, and the same amount of cooling per unit time is taking place.  While it is true that if a particular "parcel" of water goes through the radiator faster, it will receive less cooling, it is also true that the same parcel of water will go through the engine faster, and therefore receive less heating.  Thermodynamically, it all evens out.  Another way to think of this is that if you slow down the water in the radiator, as it exits it will be cooler, but then it will travel through the engine slower, so as it comes out of the engine it will be hotter.  Thinking of it in that way, the faster you can circulate water in the cooling system, the more stable the cooling system temperature will be.  If I could bolt a 100 gpm pump onto any of my engines, I'd do it.

Going reverse through the cooling system, on the other hand, makes a lot of sense from a horsepower perspective, because the water will be at its coolest coming out of the radiator, and the cylinder heads are where most of the heat is.  So, cooler water will absorb more heat from the heads than water that has already been heated somewhat by traveling through the block.  The horsepower gain is thermodynamic; keeping the combustion chamber and intake charge cooler by reducing the cylinder head temperature results in more heat extracted from the combustion process.  However, I don't know if you can just reverse the polarity of the electric pump motor to effect this change; I haven't taken my CVR pump apart to see if the impeller is directional.  I strongly suspect that it is, in which case a different impeller would be required in addition to the polarity change on the motor.

Maybe I'll take my CVR pump apart and look this weekend...

NO, I would think that wouldn't be possible. I took two aluminum mechanical water pumps apart to see the impellers.

One pump was standard rotation, the other was reverse. The impellers were different as in backward to one another. So there wouldn't be a way to simply flip them over to work a different way.

Now, what you could do is call the company and get the shaft size, and impeller dimensions for a 5.0l engine. If they are the same, and I bet they would be for simplicity, you could just swap impellers, and then the polarity on the motor.

Also, remember Mario 428 makes the alternator brackets for these electric pumps if you need one. I have one on my setup with a Procharger, and Mez electric pump.