TH350 and Driveshaft question

[jmlcolorado]

Bare with me if this is a stupid question, but im building a truck utilizing a 68 C10 chassis with factory axle on trailing arms. I have installed a SBC 350 with a Pontiac 350. I need to build a driveshaft for it and have found a 69 C10 shortbed in the scrap yard. It has a manual transmission in it. My TH350 has (obviously) a slip yoke at the output housing. The junk truck has a slip yoke built into the shaft itself and it mounted to the transmission the same way as the yoke on the axle, with small u bolts.
Can i just swap the output shaft yoke on the driveshaft with the TH350? Will it be a problem having 2 slip yokes built onto the driveshaft?

By the way, mine was a long bed, converted to short bed, eliminated the carrier bearing, and the junk truck is a shortbed.
If it is a problem having 2 slip yokes, would it be okay to weld the dlip yoke built onto the shaft solid and let the slip yoke into the trans do all the work?

EDIT: I dont know for fact the junk truck has a 3 speed, it is a manual on the floor though.