[Longhorn Man]

it can be done, but it could be opening up a huge can of worms.
The industy standard has been no longer than 6 feet long for a drive shaft. It's been that way for ever, up untill recently. now, they are making them out of alluminum and in a huge diameter. (I see them broken all the time)
if you go to a drive shaft shop, most will send you away.
Others, will do it, but charge you a LOT.... and only 1/2 of those places should try it.
The longer the shaft, the more it'll sag. It won't be measurable, but the faster you drive, the more it'll matter, and if you do the overdrive, it'll matter even more since the shaft will be going faster than the crankshaft.
If they do it wrong, it'll not just be out of ballance, but it'll 'whip' ... think of rolling a pushrod on a piece of glass. (best way to find if one is bent) Imagine that push rod has a slight bend in it... just enough to be seen. Now, imagine that as a driveshaft... weighing 25 pounds, and spinning 3000 RPM.
It would shake the truck, it would ruin the seals in the tranny output, and the diff input, and would end up damaging both if left alone long enough, or if it is bad enough, it could damage things quick.
A properly assembled 2 piece is perfectly fine. It can handle more severe angles from the engine to the axle, you can remove just the rear half for towing, which would keep the tranny from barfing all over the place, and with quality components, can handle what ever power you give it, and hold up for many years. Many of these trucks still have the original carrier bearing under them today.

Some will tell you they did it and it's fine. Others will tell you they did it, but had to kill the crossmember to fit the shaft through, others will tell you they did it and it was a waste of money.



I say spend the money elsewhere.