If you want to remain mostly stock, you will want to keep the original bellhousing (has the mounts for brake/clutch pedals) also flywheel and 6 volt starter even if 12 volt now. If you change to later starter you'll need to also go with later flywheel. I've had my 46 for over 30 years using a later six but kept ALL the 46 bellhousing/flywheel/starter etc.

Later trans will work with your old bellhousing but need an adaptor.
Best of luck

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed