I had started modifying another new stock tank after all the problems I had going to MATS. I was going to use a 255 LPH pump with the corvette regulator. On the one way check valve thing, one idea I was going to try was using maybe 4 or 6 thread in (metal) PCV valves I know it sounds weird, but they are a one way metal valve and super cheap. The one way ball valves from fuel safe made me think of this. I also was going to spend some time at the wrecking yard to see what types of flanges could be adaptable to the stock tank. In the end, my wife convinced me to get a bolt in tank from Rick's stainless. They use a metal flange they either buy or make themselves to fit the camaro ss fuel pump module.

rickstanks.com

Call and ask if they will sell the flange seperately. It's worth a shot. The camaro ss pump module is ~175ish or less online, internal regulator and return, one line out, 58 psi.

or maybe a fuel pump module flange from a LX mustang, they make everything for one of those cars.