I believe that the 79-81 trans am had the 8.5 10 bolt, rear discs(came on the WS6 package), and from what i have read so far the components should fit onto other Gm 10 bolts and some 12 bolts, dont take my word from it. I found it online today.

Yet with your 1981 El camino i caution you about the spring perches on this rear-end. You will have to cut the originals out and remount new ones. This is due to the fact that they are out to far on the housing, My car is half way through a mini-tub and will have to move springs inline about 1.5 inches as it is.

Oh and by the way i just bought one today, a 79 GM 10 bolt with rear discs, 3.08 Posi originally froma Trans am. Looks decent for 400 bucks. Also on the way is an upgrade Disc brake kit for my SS, it already has Power Disc's. But want to go new while im redoing everything.

Here is the web page

http://www.geocities.com/motorcity/6765/page11.html

-Rennskii(hopes this helps)