Rear What is It? Any good?

[red79vette]

It is a 10 bolt from a 1978 Pontiac Grand Prix.
Any idea what it is? It has square lugs like a 8.5 and a indented cover.
code on axle is R2B 3621

 

[jrm81bu]

Looks like an 8.5, but it wouldn't have came stock in a 78 Gran Prix. Are you sure it's not a 77? Those would of had the 8.5's but they are around 4"+ wider than a g-body. Or someone could have swapped it into a 78 at some point.