Re: what rearend
A 1980 Camaro has an 8.5 inch ten bolt with leaf springs that is the same as most of all of the previous rear ends under Camaros. If you have a 2.73 it will accept a 3.73 gear, but you will have to upgrade the differential to an Eaton three series Posi-Trac to limit wheel spin. You can also buy one that uses 30 spline axles instead of the stock 28 spline axles you have now to add strength.
You say you have one but are you sure it works with your existing rear end. In 1982 the third generation Camaro was introduced that used a 7.5 inch rear gear with coil springs and a torsion tube-trailing arm suspension. So I question is what you bought used to fix your problem.