We move from a single to a two piece on the 1450 truck. The reason was so that the tail shaft part was bolted on to the transmission. That way if you lose the drive-line you don't lose the tanny oil. At least that was what we were thinking at the time.
Sounds like a good idea for saving transmission fluid. I just measured it and it would need a 68 inch shaft and with a deflection calc. I find that a 68 inch shaft would not work at Higher RPM so I guess I have to stick with a 2 piece and replace my carrier bearing. It would work with an aluminum one but its not worth the $4-500 to me. I though it was nowhere near that long.
"I was thinking the exact same thing about you..."