I have a loud Holley Blue pump that I would like to replace with a 300lbs at 15psi Holley Pro-jection (670cfm projection pump). I will use a Mallory three port to utilize the return line, my question is do you think this pump would handle my ZZ4 with Holley Carb? I'm using this pump cause I bought it when I had the pro-jection. Please let me know.

See if you can find specs for the pump in gph on Holleys website. hard to say just on a guess fi it will or not.

If I had to guess..I'd say Holley only recommends that projection setup for motors under 300hp. The fuel pump might be sized accordingly, which is a bit under the zz4's hp rating.

Jester,
I looked it up on the web and it states the blue pump is 110gph - free flow and 70 gph @ 9 psi.
The Projection pump is 300 pph @ 15psi
Is there a cross ref chart for GPH to PPH?

Jester,
Here is the info on the Holley Projection pump:
300pph @ 15psi
50gph @ 15psi

Since this will be for a carb set up, I'll only need 6-7psi. Since their ratio is 50gph @ 15psi, what do you think the gph will be for around 6-7psi? Running this with a return line regulator should supply more than enough fuel for my ZZ4. I've read people using the stock pump from their TBI and that supplies enough fuel for their set up, this should be great though. Any ideas or suggestions?

50gph @ 15psi is pretty crappy. I wouldn't run that on a 300+hp motor. It might work....but it'll be marginal at best. If I were you..I'd replace the pump.