https://m.youtube.com/results?search_query=6.75”+differential+backlash
Can’t claim any personal expertise, but it is technical.
Measure, torque, check again, loosen, re-shim, rinse repeat.
I helped swap a set of 5.13 gears into a 67 GTX back in the 70’s.
You need special paint to get the gear pattern correct.
Dyechem? Been a minute and CRS has set in.
Watch some of the YouTube videos and decide if it’s in your skill set.
https://m.youtube.com/watch?v=JWAVcJVHZ28https://m.youtube.com/watch?v=dAqAqODmcj4Good luck. (I’d have to pay someone, lol)