Are the posi carriers and main caps the same in a 1969 Impala 12 bolt rear end as they are in a 1969 camaro 12 bolt ?
I found a 1969 Impala with a 12 bolt and was wondering whether these and other parts would interchange.
Thanks in advance!

Yes, the internal parts are the same. If you're going to use the caps from another case, have the case aligned bored after the non-original caps are installed.

Swapping bearing caps requires machine work. They can not just be bolted on. They must be fitted to the housing. Check the posi to see what series it is. Most of the Impala rear ends that I have seen had 2 series differentials in them.