Rear end swap
I had a 63 Nova SS and swapped in a rear from a Dodge Dart 8 3/4, the spring pads were right on and it was about 2" narrower ,u-joints were same diameter so original drive shaft worked too.I think you want to look for a 66-69 year just take a tape measure and go hunting,I got lucky and mine had the Sure-Grip posi,the bolt pattern is different 5 on 4 1/4" or 5 on 4 1/2"Good Luck!(also check 8 cyl Plymouth Dusters)