Trying to finish up my 400/470 build and have a fuel pump question. I have two fuel pumps in my stash of parts to choose from. One is a Holley 12-440-11 that is rated at 110 gph and 6.5-8 psi. The other is a Carter M6903 rated at 120 gph and 6-7.5 psi. Which pump would you choose for my application?

If they both work then I'd say it doesn't matter.

FWIW from my perspective I have NEVER heard anyone say man I wish I had less fuel pump. IMO if you EVER plan to build more power why not just start with a bigger/better pump to begin with. If its a budget deal then I get it otherwise lots of BETTER options out there

Either one should be fine for a street/strip deal, have used both and an Edelbrock equivalent.
Probably gonna need a regulator so you don't blow through the needle & seat, especially on a Carter or Eddy carb.

I've been running Holley Blue pumps for years, feeding blown big blocks, without too many problems. I do keep a spare in the trunk when I go on a road trip, but they usually last 5 to 15 years. They do make noise...adding good rubber mounting pads instead of what it comes with, will help. Whether or not this is the right pump for you, I can't say.

My memory is not as good as it use to be
Is the Carter you have the one that has screws holding the two halves together or is the upper and lower body crimp onto each other? If it Is the good two piece unit with the three valves inside use it
I've never had a Carter carb. have issues with that pump with those pressures flooding, never