The flow rate needed is related to the horsepower the engine is making, it is only related to engine speed in a general sort of way. Any standard type quality pump will keep up with your engine. The high pressure pumps you describe above are meant for racing applications and likely put out too much pressure for your standard tuned carb.
4-5 psi is plenty, 8 psi will likely push gas past your needle and seat. That is not a good thing.
Get a standard Delco or Carter as mentioned above. Don't worry about the rebuildable thing, it is unlikely you will ever need or be able to get parts for it anyway. Crimp together pumps are OK if they are quality built.
Go to a Chev dealer and buy the real deal, or get it on line, but get a OEM quality pump. If O'Riely sells Delco or Carter, you can certainly get it there, or anywhere else. You have learned what cheap crap is worth, don't buy it again.
I never use second line (cheap crap) parts on anything I want to keep working, the good stuff is well worth the small cost of the up grade.
Keep that Chevy on the road! :{)
