71 Dart, Fueltank to crankcase vent as return line?

I did very similar to what you are saying, Cope, on '70 GTX. Holley mechanical
fuel pump w/out regulator, though. My car had an existing return line, though..
Put a fitting in fuel supply line near carburetor, and ran a line to existing fuel
return. Put a Holley main jet soldered closed and redrilled with a smaller hole
in line as a restriction and had no problems. Later got correct vapor separator
that mounted on fuel pump as I remember, but homespun bleed worked fine.