I am trying to rebuild my rear diff. it is stock now and making bearing noise I think. has been for a long time and getting worse. I want swap to 4.11 gear from 3.42.
to find the correct parts do I just need the gear set and the install kit.
when searching ebay for gears I find 7.5 inch and it says fits 99 Camaro z28 and I find 8.5 inch and it says fits 99 Camaro z28. which is correct , do I need to check or is it always a 7.5 inch that comes stock in the 99 Z28 ls1 - t56?
28 spline - is this something I have to disassemble to find out before I can order parts.
do I need to replace the posi package or can I just change the gears and bearings?

separate from first subject , I did purchase a rear diff from a 2000 Camaro SS but it has higher mileage than mine so I want to rebuild mine rather than change to the 2000 SS rear and find out it needs rebuilt too.
is the 2000 SS rear different than the 99 Z28 rear end. both are t56 cars.
please help with this if you can.
Thank you.