1 - Your factory sending unit isn't setup for a return style system so its your choice of what fittings you'd like to use for your new line as you'll need to modify your sending unit for the extra line (I don't know the '66 well at all, but most carbed cars only have a fuel outlet). I would personally use the stock fuel supply location on the sending unit for the supply line (since it has a proper pick up in the tank for suction) and install whatever fitting you desire for the return line.
2 - The first thing that comes to mind is a combination of high pressure rubber fuel hose and junk yard sourced connectors. Its a junkyard build so that's where ya gotta go!
I don't mean that as an insult or anything. I've done plenty of that type of thing myself and consider it the heart of "true" hot rodding back when you couldn't do it any other way. My second thought it scouring the Dorman fuel line repair kit at your local parts store.