I like the basic Vintage Air A/C unit. It's made so most home mechanic can install it easily. If you're not an A/C person though, you will be taking it to a pro for charging.
Gears? Ha!
Lots of speculation there.
My advice is to do the rear first. After all, most of our cars aren't the 10% off-the-road like we think.
There are lots of gear sets for these. Not just the more common 3.50, 4.11, 4.88, and 5.13, but also 3.73, 3.90 and 4.30.
Don't let anyone even try to tell you what your car needs. It's an individual's feeling here that matters.