Welcome to Stangnet.
If I had to do it all over again, I would do this in this order:
1. Aftermarket shifter. Not too expensive, easy to install, a major improvement over stock, and something you will benefit from and enjoy
every time you drive your car.
2. Subframe connectors.
3. A tuner/flasher/programmer, closely followed by...
4. Gears. 4.10:1 unless you drive a
LOT of hiqhway miles.
5. Exhaust. Something you just gotta do.