Anything can be done with enough time, patience, and spare tools to throw when you get frustrated! While, it can be done, I'd recommend just selling your current Jeep and picking up one that already has the 4.0L in it. Much easier. That being said, if you've got the space and can get the parts cheap enough, go for it. I've got a '68 Camaro SS beckoning to me to work on, but I don't have enough space for it and my Jeep in my garage. One thing at a time I guess....
NVRDLMO....Here's a thread of someone that's already done it. Sounds like you're missing the speaker brackets to hook up to the factory speaker mounts. Anyway, it might be worth you checking out.
It's not that difficult. You'll need a Sharpie or other felt pen, in order to write your phone number down on one of these:
pshhh I had one on my civic for 4 months... put it on craigslist and it sold the same day
99 TJ 4.0l 5speed, Bushwacker flares, JKS endlinks, Procomp stabalizer, Procomp 4 inch lift, 3 inch body lift, edge intake, Edge throttle body, Edge control module, flowmaster exhaust, Maxxis bighorn 35x12.5x15 tires on allied progressive beadlock wheels, sony cdx-fw700 cd player, xplod front speakers, eclipse rear speakers,Olympic 4X4 Products Xtreme Duty Tire Carrier in Rubicon Black
I got a TJ 99 with 4 wheel drive sittin out back of the jail