I run the Carter 6270 on my 340. Works great, although I'm probably only making 420-430 hp. I also run a 3/8" pickup and fuel line with -6AN fittings from the pump to the regulator and carb. All probably overkill, but I needed a new pick up/sender and line so why not.
I do run mine with a regulator, and it's probably a good idea. Mine was cranking out almost 8 psi without one. Maybe not all of them will, and maybe you can get away with it, but it's easy enough to install one and then you know exactly what you're getting.
