I did some research and what came up was that the car will run rich because more fuel is pumped. So without the fuel pressure regulator it'll be using more gas.
I'm looking to replace my fuel pump because it failed and I have the walboro 255 that I was planning on throwing in when I get my other engine swapped in, but now that I'm in this situation I was wondering if I can run it on a stock setup.

 

You got it. You can run it like it is without an adjustable FPR but the fuel economy will be poor.