1972 Fuel Transfer Valve

[PbFut]

Interesting on the return line. I have a Fremont build Ca delivered gmc 3/4 ton. Commercial classification. No ecc venting but does have return lines. The factory NL2 option aux tank was plumbed with a stacked selector valve that did route supply and return fuel and had factory hard lines in place for both tanks.
30 years ago I owned a 1971 c20. It had 3 tanks not NL2 optioned and return line only to main tank. I had to do the flip flop method on that truck.