I've been using the 255 walbro and mallory 4309 reg. for years, -8 feed and return with no pressure creep problems. You are going to want a gauge to read while driving to verify the pressure is increasing with boost.
'72 Scamp, 3500#, 440, S400, blowthrough, meth. inj.
9.78 @ 139 so far at 12 psi, 11.00 @ 131 on real street tires.
