Welcome to the board victor! You've found one of the craziest automotive sites on the net.
Now for the truck: In 1950, your truck would have come with either a 216 or a babbit-pounder 235 with a 6 volt electrical system. The tranny would be a 3 speed standard with a non-syncro low. (Some trucks had 4 speed floor shifts with granny low). The rear axle would have a torque tube enclosed driveshaft and 3.90 to 4.5 something gears. Now many of these trucks got converted to 12 volts & later engines and trannies, so I can't say for sure what your truck has in it now.
The only 'newer' engines that will easily fit in place of your stock engine is a '55-62 full-pressure 235 straight 6, or a late '50s 261 straight 6. And since the 216/235/261 bellhousings are different from any '63-newer engine, you can't swap in a '63-newer tranny behind a 216/235/261. Also, the enclosed driveline requires a pre-55 tranny to work.
So the short answer is either stay with a 235/261 six, a 3 speed and closed driveline, or swap a newer drivetrain into the truck, but that will require cutting and welding on motor & tranny mounts & swapping out the rear axle for a newer truck axle.
This is just a rough overview. As you get into this and ask pointed questions, the fine points of the mechanical systems of these trucks will become apparent.
good luck and welcome!
chip
