Front driveshaft used as SYE?

I've heard on here that some newer model XJ's front driveshafts (or part of them) could be used as a cheap SYE.

Am I missunderstanding something, or can it be done? And how hard is it?

Only if you have a auto and either a 8.25 or D44 rear axle. Too short if you have either a manual or a D35 rear axle. The driveshaft must also be from a auto and you need a yoke style SYE rather than a flange type to blt right in. Can adapt to a flange is you use a flange coupling.
Here is my home made SYE for a 242. http://www.go.jeep-xj.info/HowtoSYEconversion.htm

http://www.naxja.org/forum/showthread.php?t=931467

http://www.naxja.org/forum/showthread.php?t=933440

Those should help answer some of your questions.