super swinger is underway!
One of the Mopar mags did an article where they put the Barracuda gas cap onto a Dart. I think they said they could have pretty much bolted it on by moving the filler neck to the outside of the quarter panel or something like that but they thought it looked like it stuck out too much. They cut notches in the quarter to clear the hinge & latch on the cap & filled it in with sheet metal. It looked really good. I plan to do the same on my Barracuda. I would have to do some digging to find the magazine because all of mine are currently packed away. I'll see what I can do in the next few days or maybe somebody here can point you in the right direction.
As far as the 8" Ford rear, I have a friend with an 8" behind a warmed over 302 in a Mustang II with a 4 speed. I haven't talked to him in a long time but I don't think he ever had any problems with the rear & he's really hard on his cars. If it was weak, he probably would've broken it.