Is there a linkage issue? Anything slip or get loose in the junk that attaches your shifter to the t-case (IOW, the linkage)?? that happens on 60's a lot, usually they fall out of 4WD though, not in.
I know, I'm not much help.. I'm just a button pusher.
82 fj40, 99 uzj100, 06 gx470
97 DR650, 05 525EXC, 06 TW200, 89 TW200, 09 TTR125, 07 TTR90, 07 CRF50