Needs parts source

I am finally getting the new(er) engine and drive train in my 1950 Fleetline. The problem is I need the fork and throwout bearing for the whole thing to be hooked together and installed. The block has a number or 3921968 (intake 3923418) and the transmission has GM203852645 on it. I have done at little searching and come up with nothing yet. If I have to buy new I would need to know a compatible part number(s).

Thanks in advance,
Warren

 

I believe the drive train came out of a '68 C10?