833 Gear Pitting... Help!

Well I see the ball and trunion so you have a 3.09 first gear set, 64-65 A body trans.
Looking at the rust on the case, you need a complete teardown and inspection. Brewers can sell you the gears you need after you identify what is bad. At a minimum you will need o-rings, gasket set, most likely some bearings, needle bearings, etc.
Do you have a B&T driveshaft?
After you take everything into the equation, this might not be the box to run.