Mine is always running cool. I think my thermostat is stuck open. The REM show temperatures from 170* to low 190*s with outside temperatures in the 30-40* F.
The front brakes changed in later years. Specifically, the knuckles and calipers. If your D30 has the CAD, then you may look to swap a whole axle from a later year XJ. That way you can get the "newer" style brakes and eliminate the CAD. Just make sure the gears match. You 88 manual would have come from the factory with 3.07.
As for the D44, the retaining plate is different from D35 plates. So pulling the parts from a ZJ with a D35 disk-brake set up will require modifying the retaining plate. The D44 four retaining bolts are equally spaced (like a rectangle). On the D35 plate, the two top bolts are closer together than the two bottom bolts. I have seen videos where the plate is drilled to change the bolt hole locations (see Nickintime youtube). There are disk brake conversions for a D44 that have the proper plate.
Yr?
If RENIX, the do Cruiser's Mod's first.
Look in to getting Nick-in-Time-Design "Renix Engine Monitor" (REM).
Mine had a somewhat similar MPG issue. Turned out I was stuck in Open Loop - bad O2 sensor.
Did you connect the Crank Position Sensor (CPS)? It is at the back of the engine, close to the firewall. It's two wire (three socket connector) that drops down to the transmission bellhousing.
Fill in your profile: Yr, engine, trans, 4 or 2 wd, package (sport, pioneer, Laredo, etc.), and you location. I know you put it in your original post, but that will scroll off the screen in no time.
Welcome to the addiction
You need to check out the thread in the DIY section. SCJ Steve has a discussion on Key Parts floor pans. He also has a U-Tube channel where he is refurbishing his MJ.
You can search your area for a company that does electric motor rewinding. If they can't help, they may know a company that can.
Good luck. I have a DeWalt radial arm saw that was my dad's. As long as I can remember, it was in our basement. I was born in '64, so it is probably sixty years old or more. It still works fine (for what I need from it).