Here's a right up on mine.
http://infohost.nmt.edu/~jscarbro/driveshaft.htmI have used it for awhile. It is very stout, and works very well. It has around 11 inches of total travel (8" slip,3" compress).
The zerks got ripped off before i even took the time to grease it, as i expected.
I have rear springs up front and didn't have them clamped, and when in Moab, i got enough axlewrap to pull the shaft apart. Other than that, i haven't had any problems...