How did you run your fuel return line to fuel cell?

IMO, -6 seems a bit small. Either use -10 or -8 from your fuel tank/cell. Use the -6 for your carb feed line, and -8 for your return line. Someone else on here might chime in with more info on this issue. IIRC, Barry Grant's web site had some illustrations on the feed systems for electric fuel pump/carb set ups.