As I understand it, it is the regular GM 10-bolt, same as used in most of the RWD offerings for the past 20+ years (including the Z-28). There were a few exceptions that had a heavier 10-bolt (Buick turbo Grand Nationals, and a couple of others), but they should be fine under an AD unless you are a drag racer. My '97 Sonoma with the 2.2L four and OD automatic has a 4:11 ratio, if you need deeper gears. I'd guess that 3:73s could be found too.
I've got an article from Car Craft around here somewhere that explains the variations - let me know if you want it and I'll try to dig it up.
The width sounds pretty close - I've heard that a 70 1/2 - '81 Camaro rear end is ideal, but I can't vouch for it myself.
---> Bill