Technical 1950's pontiac question

Hi all
i have a pontiac straight 8 with a manual transmission and im wondering a few things
1. is there a rebuild kit for the manual gearbox/transmission
2. to lower the rpm at highway speed should /can i run a hydramatic diff centre 3:08 instead of my higher diff which came with the manual gearbox cars.
3. where can i get a kingshifter for my gearbox
cheers josh