OK 46Burb the best solution is to go with the T-5 S-10 overdrive trans that everyone on this site is yaking about. I've made the switch in my 46 pickup and it's really sweet. With the 46 you have a smaller trany pattern between bellhousing and tranny, easy cure which also aids in swapping in the T-5, is to contact Buffalo Ent. for an adaptor plate. You will need this adaptor with any trans you use.
Buffalo Ent. is in WA State phone 360 652-7684.

Also you easiest rear end to go for is from a 55 and later pickup, most were 3:90 ratio and should be easy to find.

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