TLDR: ICM needed a good clean and the pins needed to be brushed up and polished with sandpaper to remove corrosion. Tried many things prior to this to no avail.

First off, I'd like to thank everyone that was patient enough to help me out as I learn more about cars, especially the XJ. Hopefully this write up helps someone in the future with an issue similar to mine.

To make a long story short, I have an 87 XJ which after an oil filter change, mysteriously stopped starting. It cranked but did not start. With the help of many people here, I started investigating. I found out there was no spark when cranking as well.
I first started with the CPS which is the #1 cause when searching forums online. I first tested my CPS and the resistance numbers were off - OL. I went to OReilly and bought a sensor, put it on, and still crank no start. I read again that aftermarket sensors can be bad out of the box so I went to NAPA and I got one from them after reading their sensor parts tend to be of better quality. Same issue: crank, no start. Maybe my multimeter doesn't pick up such small AC voltage but both of these sensors kept reading 0.0 volts when cranking. This led me to believe that maybe there was something wrong with the flexplate. I opened the inspection window and the flexplate moves on crank so I had no reason to pursue this further.
I went to Cruiser's page and I made the modifications to the mounting holes of the CPS. I made them a little larger and pushed the sensor in while bolting it in. Still nothing. No voltage on crank, and most importantly, no crank.
Following Cruiser's page, I also went ahead and cleaned the C101 connector. I spent an hour or so going through it and cleaning off all that muck. Still I got crank no start. I then dug further into Cruiser's page and refreshed grounds. They're not perfect but they check out and are now better than they were when I got the car. Still no change.
It had just been my birthday and my parents were gracious enough to get my a Haynes manual. Along with the FSM I found online, I went through the ignition system. I found that the ignition coil didn't pass the resistance readins and I was able to purchase a Delphi one on Amazon for pretty cheap. I installed that and I noticed the ICM had pins that looked blue and corroded. Silly me, I didn't think much of it. I put the ignition coil back in, and still nothing.
I went back to Cruiser's page and lo and behold there is an ICM/Coil page. It specifically states that at least once in the lifetime of the vehicle, the connectors should be sprayed with electronic cleaner spray and THE PINS PUSHED TOGETHER AND ROUGHED UP WITH SANDPAPER. I was so convinced in my head and so tired of the issue that this time I begrudlignly dug in my garage for sandpaper and gave the pins a good clean. Then with needlenose pliers I squeezed them tighter together. I had some dielectric lube/paste so I put a small amount into the positive and negative pins of the ignition coil.
I put it all back together, turned the key and it fired right up. I cannot describe the feeling of elation.

Anyways, I hope this helps someone down the road as I haven't read it many times out there with this issue specifically. I was recommended by a few folks to look at the ignition coil but not to clean the ICM as an added measure. Highly recommend doing so before spending more money elsewhere.

All in all, I was able to do this with 2 CPS replacements (the first one may have been good but my multimeter may not pick up such a small voltage), and a new ignition coil. All in all about $60-$70. I've read of other people having issues with their distributors, cap, and rotor but before going down that route, I suggest cleaning the pins and connectors of the ICM.

Thank you all! If anyone in the future has any questions, please feel free to ask/comment.

 

Congrats!

Please go back and close your other threads on this or others will keep responding. Thanks.