Unless the transmission you're using is a LOT longer than the one that was in the truck originally, you're headed for a truckload of trouble trying to stretch the driveshaft. There's a reason for using a 2-piece shaft, (length of the frame/chassis) and unless you believe you're smarter than the engineers who built the truck it would be wise to stick with what it was equipped with originally.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!