The front is a direct bolt in, the rear will have to have the spring perches moved and the shock mounts removed, but it is the same overall axle as an XJ
Ah, Pete beat me to it! Haha
I've come to like the Falken Wildpeaks. I have the orgional style on my 96 XJ with over half tread at 40k or so miles on em and have the At3 on my 99 Xj. Great both on and off road.
The cable driven gears do have to be in a certain way to work.
My rebuilt 231 also makes a slight whine while in 4 hi. As long as it doesn't jump outta 4wd and you have no banging/clunking I wouldn't be concerned.
You can still find new Renix manifolds on ebay for $100-$150
https://www.ebay.com/sch/i.html?_from=R40&_nkw=87-90+Jeep+4.0+exhaust+manifold&_sacat=0&LH_TitleDesc=0&_sop=15
May have to trim the corners of the front flares but otherwise you should be fine. On the street that is, likely would rub if the suspension started cycling.
Robby Gordon has done nothing but great things with this series since it premiered in 2013. Also fun to watch and alot of great talent is drawn to it. Wish it would have more of a presence in the eastern US though, I'd love to go watch!