I will be swapping a different rear into my Firebird soon. The rear has a hole in the top of the differential/gear case for a 3-channel ABS plug to be placed into it. I don't have ABS on this car and just want to bung this hole.

Anyone have one of these (working or not) and willing to sell?

go down to your local parts store and look for a freeze plug emergency repair kit. it should have a rubber plug w/ a bolt thru it. as you tighten the bolt/nut it exspandes the plug. not sure if they make them that small, but its a thought.