I don't know who told you that a Holley will take 9-10 psi, but he should be tied to a pole and caned.
Tee off at the carb inlet and run a copper line back to the firewall, then up past the hood lip and onto the cowl. Temporarily mount a liquid-filled, 0-15 psi mechanical fuel pressure gauge onto the cowl with tie-wraps or duct tape or whatever. It's only temporary until you get the pressure under control. Old Stromberg 2-barrels would withstand about 2 1/2 psi, modern day 4-barrels will tolerate between 5 and 6 psi. Don't just put a regulator in the system until you rig up this gauge and can monitor the pressure through the windshield as you drive. Pull it back to 5 psi and I think you'll have a completely different critter on your hands. Any more pressure than that can blow past the needle and seat and blow raw fuel into the intake manifold, creating a tuning nightmare. A carburetor is a carburetor, not fuel injection. You cannot make more power with a carb by raising the pressure.