Here is some info from a similar thread/discussion.
Originally Posted by Grigg
Driveline Set Up
http://www.stovebolt.com/techtips/driveline/setup/index.html

Allowable shaft length is a factor of tube size and RPM mostly, it's covered in the manual with lots more detail. The basic idea is keep it short and stiff enough to not turn into a banana at speed.
..if it had a two piece shaft before very likely you need one again. Your OD transmission increases driveshaft RPM over engine RPM, two piece shaft (shorter than one long) might again be ideal to cope with the increased speed.

General rule of thumb (with single shaft) is the transmission and rear axle pinion are parallel. More details, situations (like two piece shaft), and reasoning in the manuals linked above.

Then because the links to the manuals in the tech tip are temporarily broken search for the manual numbers to find the data, and or try these links.

http://media.spicerparts.com/media/details/kH7StMRqGZ9kzxSZM

http://media.spicerparts.com/cfs/files/media/R43pySn3ew5wA2BHs/tcfp0088.pdf

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