8 1/4 swap works. 8 3/4 can get expensive. Another option is what I'm doing, a Ford 8 inch. Ford guys swap them out for the 9 inch, but they are plenty strong enough for a slant six, moderate small block. Have to do some looking, but they are almost a "bolt in" swap to a Mopar "A" body, and parts are readily available.
The one I'm using is from a 1975 Maverick/Comet with a V-8. Spring perch is 43 inches, width flange/flange is 56 3/8 inches, 5x4 1/2 bolt pattern, and 10 x 1 3/4 brakes. Need to either modify the end of the driveshaft to take a Ford U-joint, or mix and match two u-joints to use the stock drive shaft. I'm not sure, yet, but it looks like the mopar e-brake cables will work.
PS: I'm going to be running 4:30 gears with a mini spool.