Not sure how techy we want to go but here are a few more
Lebaron hood vents are always a favorite.
A ZJ pitman arm is a 1 inch drop over stock.
97+ mirrors are direct bolt in to older XJ's and allow you to fold them in on tight trails.
MJ's with buckets had brackets that allow you to tilt the seat forward and will bolt right up to older XJ seats (not sure about newer).
Dodge Ram vans brake lines are 12" longer for big lifts
ZJ gas tank skid can be modified to fit 97+
Most 4cylinder and v6 Xjs have 4.10 axles (some with 4.56)
96-98 ford taurus dual electric fan to replace the mechanical on the 4.0
350 or 351 power steering pump (for oversized tires) with a little welding
ZJ and WJ stock tranny coolers with stacked plates (even an upgrade for us with the stock fin style)
Camaro spring isolators give 1.5 inch lift in front
GM power antennas replace your broken XJ's with little modification
5spd crossmembers give 3/4 inch tcase drop on autos with no loss in ground clearance
You can convert the closed system to open without replacing your radiator by using the fill cap from a 4.7 durango or dakota, cutting it into your upper hose, and replace your bottle with an Mj overflow tank or any that fit. Then cap off or eliminate the T'ed lines in the heater core.