I have an '82 Camaro SC with the stock 2.73's in the rear end. My roomate has a complete 3.23 Posi rear end from his '77 TA he will give me if it will fit. If it will fit can I just swap out the center section ( I just had my whole rear end rebuilt so I'd like to keep that) or would I have to swap the whole thing

 

I won't work, your '82 has a 7.5 and the '77 should have an 8.5.
The '77 also uses leaf springs and has no torque arm mount.