If you go with the lower pressure pump you shouldn't have to run a regulator. I don't on mine.
I'm not sure the specs on a stock pump but I'd worry it might not supply enough to feed a 400 hp engine and go lean on the top end.
Holley also makes a good mechanical street pump that you don't have to run a regulator on. I think it's rated at 6 psi. which is what a Holley carb should be run at for optimum perf. If your uncertain about the Carter check out the Holley.