'72 LWB with 700R4-Driveshaft ???

[fatfords]

I posted this in the "engines and drivetrain" forum, but thought I might get some useful input here, also.

I bought a ’72 LWB with a 350 and 700R4. I replaced the motor mounts this weekend, and noticed the carrier bearing was very loose. After a closer inspection, it looks like the transmission was installed without shortening either driveshaft, so it looks like that is my next project.

I searched the archives, but did not find any information on which driveshaft to shorten and how much to shorten it. The truck originally had a TH350 and is using the forward holes for the front motor mounts.

Based on this information, I plan to shorten the propeller shaft by approximately 3”, since that is the overall length difference between a TH350 and TH700R4. Anyone see anything wrong with the plan? Am I overlooking something?

Currently, the shafts are all shoved together and there is no “slip” at the end of the propeller shaft. It is so tight, that I can’t get the U-joint out of the rear end yoke. Is there an “ideal” amount of travel that should be allowed by the slip joint? Or a "minimum" length that the yoke should normally cover on the slip shaft?

Any help would be appreciated!
Thanks,
Kent