Jon,
I'm pretty new at this but I found a web page on Hemmings that might shed some light on your number behind the distributor.
http://clubs.hemmings.com/clubsites/chevytalk/GMhistory/1933motors.html. According to this info the T prefix would designate it as a truck and the number
3795778 seems to fall into the July 1933 production numbers.
The 216 was not introduced until about 1937. Perhaps you have a 207? Someone with more knowledge than I will have to help you with the definitive ID of your engine.
Perhaps you can email a picture of your old waterpump to your supplier and they can help ID the pump for you if the engine was really built in 33.
I hope this is a step in the right direction.
Randy
