3 Speed to 4 Speed Swap Questions

[Hawks]

Hello, been a while since Ive been on here, work takes all my time, Ive been driving my 60 like crazy and getting ready to swap the motor out, (305 done wore the cam down) but i still cant kill it, Been driving it like this for months, it will pop back through the carb at high rpm, So im swapping in a 350 im re gasketing now, I plan to change out the 3 speed OD with a truck four speed, Its a c20 custom camper, Its a wonder i haven't grenaded the little 3 speed with all the abuse it takes, My main question is i now have a one piece drive shaft and i would need a two with the truck four speed, where would i mount the carrier bearing? I don't have a two piece drive shaft in my parts trucks so i may have to make one from a 73-87 truck work, Any info will be great, Thanks