Hi KGROVE, I appreciate all the detail here on what you went through. I have a '92 LJ (with a swapped KZ) and don't have a dead tach, but one that's very sluggish. Will be tearing it down and will look to see if the springs are off. More soon...
RE your ebay purchase. Was it US ebay or another...
I did this last year on my '92 LJ78. Any double din will fit. Mine arrived from Japan with an aftermarket single din stereo already so just make sure you get a harness. Anywhere you buy the 2din head unit can help you with the harness.
I highly recommend Alpine. I first spent $350 on a Sony...