A TC drop is a cheap and temporary means to reduce driveline vibrations following installation of a lift kit of 3" or less. Depending on your other specs, you would need an SYE kit if you lift beyond 4".
If you really want to fab up a TC drop, you'd first need to determine what size drop you want. Every Jeep is different and the variables come from year, type of transfer case, front differential, rear pinion angle, etc. A 1" drop might work for some, and a 1/2" drop might be best for others. You'll want to figure that out before expending time, money, and materials. (By the way, your 2001 XJ implies a low pinion Dana 30, which will be greatly different than say a '99 XJ with a high pinion Dana 30 differential).
Also, transfer case skid fitment may depend on the TC drop you add. I suggest either eliminating the TC drop and going for an SYE installation first, or building a TC skid that can accommodate a drop from .5 to 1.5 inches. The ironic thing is the more you drop your TC, the more you need the skid.
Good luck.
