Yup, it was me!
As Peter says, you need the AX15 from a diesel Cherokee or Grand.
If your '99 already has an AX15 (it should have, unless it's an auto), you're laughing.
Pull the old box out and remove the rear housing (where the t-case and gearlever bolt on), and swap this onto the diesel box. This will be obvious when you look at them side by side, the bolt holes for the t-case are in different places to clock the box more horizontal to clear the bash plate. Then, bolt it back in and go play
While it's out, throw a new clutch in there. Use a 4.0 clutch, not a diesel!
Just a note for anyone else who may be interested, if you're banging a diesel box into a YJ, you can replace that stupid, leaky POS internal slave by using a diesel bellhousing and external slave, same as a post '94 YJ and TJs
