I'm probably going to sound like a Grandpa here, but why waste your time on a Ratrod when you have the makings of a super cool rod in your driveway! That 2dr would be cool anyway you build it, custom, rat, hot, you name it, it will be cool. I would use the Cougar rear if it measures up all right, maybe all the running gear from the Cougar, just to be different and keep the costs down. IMO, the Chevy frames from those years are best suited to those years and would make a poor donor frame. Be rid of the enclosed driveline and start up fresh with rebuilding what you have on the chassis. There's got to be some good info on making that frame usable for a street rod. Good luck, I would love to have that 2dr. but I can't seem to get done my own project!
"When I was younger, I could remember anything, whether it had happened or not." - Mark Twain