Main case and GEARS will allow a new extention housing and shaft to be swaped. The key is you must get a NON overdrive mainshaft to use with a housing. Bearings are not the problem, you can use either 308 or 307 bearing front/rear. The early gears cant be used on the OD shaft.
Or just start with a real A 833 trans.
Which I happen to have, rebuilt even, for the large yoke.