While not an engine update, I installed the 4.56 gears and the mini-spool into the Firebird. While the axles were out I checked and they fit nicely in my old 8.5" rear end with a true positraction and 3.42 gears. If things go south with the mini-spool and it doesn't take an axle out I can swap the rear end assembly if needed. I really want to run this engine with these gears! It'll be 3,000 rpm at 75mph with the overdrive.
I thought the stock Firebird rear axle is a 8.20? Did you install a later model rear axle?
