Kevin, Sounds like a Jeep problem..hehehe. Sorry dude, you walked right into that one. I like the new rig though. Definately a sweet foundation for the next project. You change vehicles like most of us change our briefs. Chu's Jeep looks great too. Later. Also, I want you to come check out a CJ. Email me soon.
Yes, the upgrade works on YJ's up to 90 (91 uses a different motor). I just did it on my 90 and put a new heater core in at the same time. I used the stock replacement from NAPA, which is the larger motor.