Lots of stuff in this question, sorry if my response is a bit of a book
1 - An FE is usually in the car at about 3 degrees nose high (compared to the frame), less the rake of the car, so you are generally going to be level or slightly tail low. It will change but unless you are building a rock climber, really no reason to worry about temporary conditions
2 - An HP pump, off idle, could easily flood the top end. To get to the higher pressures an HP allows with the tight relief, it has to push more volume, although what really happens is it just keeps pushing until the relief pops, even though it hasn't got the tall gears of an HV pump that ends up in a higher quantity of oil up top.
3 - Not a lot of FEs will idle with the v/c off without dumping oil over that short rail, and I would say less would allow you to come off idle and not make a mess
4 - If the oil isn't hot, it's going to be a bear to get back to the pan
5 - I agree, the pegging of the gauge is indicative of an HP
6 - Depending on head design, returns can sometimes need some help, or can have a glob of silicone in them if overzealous
7 - Of course Brent is correct if you are oiling through pushrods too, you'll never get there. He watched me empty a pan on a dyno at 3000 rpm cam break in, I likely was pretty comical when I pulled the dipstick, saw it was 3 quarts low, and looked on the floor for a mess. When there wasn't it took a second for me to figure out what was going on, I was feeding from both the rockers and the pushrods on my truck motor. What the ironic part is, I popped an oil filter on the same dyno due to a stuck relief, in my mind was, "Oh crap, don't mess up the dyno room again" LOL
So, a couple of things.
- Watch your oil filter. I was young when I ran an HP in my 390 F100, it worked great and over the years that truck was happy as a clam, however, cold or thick oil can pop a filter. I ended up running 10w30 back then and over time could sneak up to 10w40. I try to avoid HP pumps when I can now
- The thinner oil drains back nicely too, might help with just a swap
- I wouldn't restrict more than a 60, and that is even pretty brave to go there, but with the oil you are moving it may work. Where it gets squirrelly is the rockers farthest from the oil pedestal. Each rocker is a leak, and if they are factory rockers, the farther you go, especially with wear, you could easily have a dry one if the volume isn't there
- Tins may help, but never hurt, but might change geometry a little if you have already corrected or checked
I would take a thin screwdriver and see if you can work through every return, if you can and see that it's adequate with a flashlight, consider changing the oil to something a little thinner, both to give the oil pump drive a break and help drain. If hot oil pressure is good, you are good
If you decide to change the pump, get to know hot idle oil pressure first. If the idle pressure is good, you can go standard, but I tend to like an HV because it gives a little better idle oil pressure. Either an HV or STD will be less at RPM though, standard 5-10 lbs less than HV and the HV will likely be 20? less than the HP. If you know bearing clearances in the engine, that would likely make a change in pump easier, but odds are an HV is a cheap fix if you have an HP now
Of course, it could be no issue now either, but that pegged gauge would want me to give the pump drive and the filter a break