Rebuild kits for the 6.5 are pretty high.
I have a 95 K3500 SRW that I got with a knocking 6.5TD in it. It actually ran and drove when I got it, but bad knock down low.
I used a 96 c2500 5.7L as a donor and did the swap.
I used the 4L80e that was in the truck, but use the torque converter from the gasser. You don't want the diesel torque converter behind the gas engine, stall is way too low.
The big problem I see with your setup using the carb is you will have to devise some way to control the 4L80e. It has to have some kind of electronic control. The standalone kits for it are pretty expensive too.