Yes you are correct on the reason for a return on a fuel system. It is to easily regulate system pressure.
I looked back and saw your carb. It appears that’s a pre73’ cable pull carb and I don’t believe adaptable to a return.
Yes sounds like the later trucks( maybe at the introduction of 2F) they made some changes and I’m not sure I spoke on the right year. I found a year specific emissions factory manual on eBay that’s been helpful for my truck.
Question1 answer: I believe the vapor stays in the expansion tank and is suppose to subside with fluctuations of temp and just simply stay put and level off via the venting gas cap.
No2: I don’t quite understand but you basically have two lines from each expansion tank in the rear quarters...
You can leave the guides loose and run the window up and down and find the best spot they need to be in depending how the glass is fitting against the seal in the upper portion. Then tighten.
There is adjustment on the tracks on both sides of the windows. Silicone spray is a good lube for the guides. Also I found the motor will draw extra amps as the window gets tight and will pop the circuit breaker under the dash as you roll up and down. Mine still does. That’s mostly from an old...
It’s very true about can’t helping from constantly making constant changes to them. Keep the thread going and keep taking pics and posting. Cool truck!