If I was you I would look into a slip yoke eliminator for your rig. That way you won't have to worry about a spacer.

that must be an adjustable length driveshaft arrangement?
i will try and find info- have you experience w/this?
must have to modify t/case output shaft to do this?
i am vaugely looking for a later model transfer case to play with- seems the only way to change my gearing.

It is a t-case tail shaft conversion. The t-case out put yoke slides now, if you convert it then your yoke will stay in one place and the drive shaft slides. My jeep has been converted, I use a double cv drive shaft.

Jus' sayin'