Shift fork is in your front axle and likely not the problem. I would guess you wore the shift mech inside you 231. What kind of mods do you have? I'm guessing a body lift or a t case drop? On a YJ those don't become a huge issue, unless the body prevents the shifter from going all the way back. Then you get 'half' enguaged in 4lo. You'll likely need to rebuilt the case. But look first to make sure you shifter is free to move though it's full range. If not, open up the floor so it can.
No sense rebuilding just so you can break it again.
Jeep: Pioneered by a war, popularized by AMC, revived by Chrysler, jacked by some Germans, and copied by all.