Tuning a Proform/Holley carb, what parts and tools?

Patience? No problem. Been there. :)

If the gage isn't trustworthy, go by the fuel level in the bowls. Getting the level stable is really important. If the level is rising the bowls, then maybe it really is getting to 8psi because that's higher than most needle and seats can tolerate. I had a problems with fuel delivery for quite some time and switching to a pump (mechanical) that was capable of exceeding 7psi when letting off the throttle or idling caused flooding at the most inconvenient times. Of course I didn't realize this at first. I have pressure gage that mounts on the cowl but don't leave it on for every day use as its not waterproof. Took me several years before I put the common factors together and realized it was the pump.

In your case, if the level is not stable then with a regulator and I assume an electric pump, its probably the regulator or vapor. If there's an inline filter, having the outlet higher than the inlet so the vapor escape. Took me a long time 'discover' this little detail of factory engineering. Discover meaning a sentence in some book setting off a light bulb, not some great discovery!