IT can be done but the longer the shaft is, the bigger the diameter of tube must be used to avoid harmonic vibration. I had a new shaft made for my '53 Chevy pickup king cab project and even though the shaft is only 12" longer than the old one, my drive-shaft guy (every reasonable size town has one) made me go up one size in tube. Take the vehicle down to your local drive-shaft guy and get his recommendation.
I had a 73 chev pick up that had that double drive shaft thing with the hanger bearing. It worked ok except when pulling my stock car trailer. Went through like one hanger bearing a season. As for can it be done I am pretty sure that they made a stock one piece version. I don't know why the two options but I am sure I was crawling around looking for some other parts in the local junk yard and saw a stock one piece set up.
Had a 73 1/2t 2wd, 250, tree-3. When I got it, it had a 1-pc driveshaft. No evidence it was ever a 2-pc. Until the shaft gave up on me one day. Checked Hollander index. The longest shaft GM showed was several inches shorter than mine.
Sold it to my neighbor, and he drove it over a year, with 1" of whip in the shaft, until he broke the tranny, bellhousing, and ripped the center out of the clutch.
That was the long way of saying, "Why not it's been done before."
Ratchet,the one you saw was it maybe on a truck with a shorter wheelbase?I had a 69 C-10 long bed and it had the carrier bearing set up.My bud had a 69 step side short bed and his did not have it,his was the typical one piece.
I have an "82 Chevy C-10 pickup and found out the transmission had been changed from the original TH-700R4 to a lockup converter TH-350, the previous owner had no knowledge of it and said one of the other previous owners might have done it.
The driveshaft is at a long enough length that the nationally known online driveshaft places won't or can't make one.
One quoted me a price of $1200 for a carbon fiber shaft, I said I didn't want a driveshaft worth more than I paid for the truck in the first place.
The local driveshaft guy, on the other hand, when I went to see him, said I could get almost anything I wanted. While I was there I watched him heating and rolling a large section of 1/4 in steel plate, after I asked what he was building- he said it was going to be a driveshaft for a cement mixer, the one that goes in between the tandem axles to drive the rear axle.
He built mine at a weld-to-weld length of 63 7/8 inches for an even hundred.