What are you 32 c-dan guys have for a back seat? I took out my gennie floor and put one in that has a kick in it so I could get the car low to my liking I also installed a small set of tubs so I could have alittle more tire(i have 43.5" in between tubs). I know a original seat frame will not work.
Repro frames and springs are available. It should be an easy job to section those to fit. If you are good with wood, just buy the spring and make the frame from scratch.
I made one out of plywood, bottom and back. While at it, I spaced the back out 4 1/2 inches and put a space saver spare behind it. Built the bottom raised so there is storage under the seat. Paddings a little thin, but nobody really sits there anyway. PM me and I can email photos to you. Oldcarmike on here padded them and covered in leather. Worked well.
Last 2 deuce sedans I did I just finished off the area without a seat. Just my wife and I. It worked for luggage, cooler etc. Put a short package tray at the rear with an easily removed front piece so I had a place to hide tools, cleaning stuff and the battery.