two a body rear ends for one

i have a early 8.75 & a 72 7.1/4 i would trade straight up for one a body 8.75 for my 72 duster the 8.75 that i have is a 64 model that has the bolt on spindles the spring perches are 44 inches from center to center it has a 2.76 gear in it not posi. i just want a 8.75 that i can install & get my duster on the road before winter thanks dale