Yeah, I was gonna offer advice til I saw the Chrysler part.

But I guess since I do own an(inherited) Ford product I will offer my 2 cents. A front crossmember from 71-87 C10 will bolt in & give you discs. PS from same truck using a REZ kit. the rear you have is pretty strong, & an Eaton posi will do well. You can also swap in a 73-87 rear but need to re-configure the mounting perches. My 350/700R4 in my 64 gets 18 mpg, not sure if that is possible w/o the overdrive. Brian