The real answer is can one long shaft withstand the speed you will be turning it?
http://www.stovebolt.com/techtips/driveline_setup.htmlThis Tech Tip has links to Spicer Driveshaft manuals, and they can help you figure the critical speed for the long shaft you are considering, and then you will see if a long shaft will work, or if you need a two piece shaft still.
The manuals will also help you double check the angles to be sure the driveshafts are installed and setup right for minimal vibration and long life.
A driveshaft can only turn so fast before it is no longer stiff enough to resist turning into a banana and leaving the truck.
Note: you want the driveshaft to stay in the truck
Contributing factors to critical speed other than speed and length, are material, wall thickness, and diameter.
For your figuring, you most likely have Spicer 1350 series U-joints in your original shaft.
I think (a rough guess) you should keep a two piece driveshaft, even if the first one is only about a foot long. If you want to use factory parts use 1 ton driveshaft and carrier bearing, having them shortened as needed.
New shafts will probably be easier if you don't already have what you need, and you can adapt a new modern carrier bearing.
Grigg
