FWIW, if you're running a plain jane little Holley red pump, that's probably not enough to keep that think fed much past half throttle...5psi is pretty low for fuel pressure-even to a carb. I recall reading more than once there should be at least 6psi @ WOT...if you're not at least meeting that, you may be running into fuel starvation.
But, while you're thinking about it,
Could you elaborate what horsepower you are getting out of it? peak and avg numbers-post dyno sheet if possible and plenty of folks can probably help you
Was the cam degreed?
What kind of 750 carb?
What A/F ratio did your dyno run show, or did you have a wideband hooked up?
What intake manifold? If I had to guess, 1500-6500, you're running a hi rise dual plane...with a 347, you could probably get away with a single plane
Also, I understand you just put this engine into your car, hence why it's in the engine swaparoo forum, but this really sounds more like something that should be posted in 5.0 tuning where more tech saavy people can see it...