GM Axle Posi Unit Interchageabilty

[72step]

My cousin has been wanting to swap in a oem type Posi unit into the rear of his 1972 Chevy C10 pickup, and I'll be helping. We've both heard different stories as to what interchanges. Some say it has to be from the same type of 67-72 Axle, others say certain GM carriers will interchange and fit all the way up to the 80's and early 90's as long as it's 12 Bolt. Does anyone have in info on this? If a posi unit will fit from the 73-87 it would be easier to find a donor from a junkard or something. What fits? What doesn't? Thanks.....

PS: I know on Chrysler Axles and Dana Spicer axles many of the carriers interchange from 1960's up to early 2k's on certain parts. I'd really just like to get the down low on GM carrier/axle parts interchageabilty. Many Thanks in Advance!