rear diff question

Is an 8.25 out of a 99 XJ a direct swap into a 91 XJ replacing the D35? Or at least minimal fabrication required?

Should be a direct swap. Searches help, it has been answered many times.

Should be.

Just get new U-bolts cause the tubes on those two axles are different thicknesses.

Yes, direct swap. If you have very little lift you may want to get the driveshaft (but not slip yoke - you'll be swapping yours on since you have the 95 and before slip yoke design) from the same vehicle as well, because the d35 housing puts the pinion U-joint an inch closer to the axle and so the rear driveshaft may be long enough to bottom out the slip yoke with an 8.25 connected.

Thanks. I have a 3" lift. I found the 8.25 for a good price, it's welded and includes brakes.