Yea man! That fold down rear seat is a cool option. I had mine about 35 years ago. Fun fun fun car. I would hand out regular beatings to my friends. The best beat down was my buddy who’s 350 Buick was otherwise the fastest car of the group and he started to talk some smack. I smiled at him, raised my hand to break into his babble and said, “Joe, I think you need to shut up before you get embarrassed really bad by my lowly 318 Duster.”
He paid the price!
The 8-1/4 rear is quite durable. I’d have no issue putting an honest 400+ HP to it and not worry a bit. You can still get brand new suregrip and other type positive traction differentials. As well as gear ratios. They’re not as wide spread as they used to be but there’s still a small gaggle of ratios and parts for them available new. I believe you can get ratios from 2.76/2.71 to 4.88’s.
Check the 8-1/4 / 9-1/4 parts at
Drivetrain :: Other Mopar/AMC
and/or
Summitracing.com for stuff.