car tires don't have such restrictions. I had directionals on my old minivan and rotated them as normal tires. at best, the maximum mud traction might be with them in the forward direction. but pavement doesn't matter.
for a rear shaft, your local driveshaft place, or adams driveshaft or dennys driveshaft online will make you one better than stock.
for a front, that's shared with XJs of the same drivetrain so I'd source a junkyard one.
If you're alone in a junkyard and you use the wire-saw method for extraction it is super-duper easy to accidentally cut into the B-pillar plastic. It's also possible to NOT do that so I'm just saying be careful.
I was this many years old when I learned Crown was making them. these are just random ebay auctions. feel free to hunt down other sources.
https://www.ebay.com/itm/133356521856
https://www.ebay.com/itm/192048200216
the manual transmission MJs most definitely do not have any device that prevents you from turning the key while the shifter is in gear and thus letting the starter move the truck forward (and eventually starting said truck and driving away). very handy technique when your clutch fails on you.
so I noticed that the HB was suuuuuper close to the timing cover and so I stuck a 5way in there and I can pry and cause the HB to move forward. this is a bad thing, right? time for a new one? the rubber thingie seems to be falling apart. I'm going to put a new one in.