7000 black belly stuck in 4th

Update, the tractor is still stuck in 4th gear.  He started it back up and tried driving it short distances to get it out of gear, but the shifter is about in the neutral position still, but not quite far enough that it is free to turn.  I told him tomorrow to try and unhook the cables from the shift tower and see if the lever moves then.  I figured if the shifter goes through the motions fine with the cables unhooked, it is probably something jammed up in the shifter tower, otherwise, it is something broken on the cable end.  If anyone has seen this before or something similar and can give me some good advice to pass on, it'd be much appreciated.

Yeah, he has the floor pan out and I think he's going to send me some pictures of it tomorrow so I can see what exactly he's looking at.  I've seen the shifter tower before, but haven't worked on it, so it's been hard for me to visualize what he's seeing as he's trying to get the thing to pop out of 4th gear.  I've had it do something like this to me once before, but it just took a good tug on the T handle lever and all went back into place... I'm wondering if 2 forks are hung up or something like that?

Dr, I'll be sure to pass that information on.  He was thinking both of the linkages motions were transferred by cables.  I'm hoping it's just a simple broken linkage and nothing serious, as he doesn't want to have to take the shift tower off while I'm gone at school.  If it is doing what I think it is doing, the shifter has kind of "slipped" out of 4th gear, but the transmission is still in 4th gear, and now the shifter is pretty much just jammed up.  I'll be sure to post an update on here when I find something else out new. 

Current Update: I had him take off all the linkages from the shifter rod (the thing going into the shift cover that slides in and out and rotates to actuate the different forks) and try to turn it with a big adjustable wrench on it, making as sure as he could it was in the center detent (the 3-4 selection) position.  That did nothing and it is locked tight, as in it won't rotate or slide in or out.  He has all the bolts out of the shifter cover and last I checked was still trying to get it to pull off, but it looks like it has been taken apart before and someone used blue silicone on it, so now it is stuck pretty tight.  The plan is to get the shift cover off and inspect all the forks, manually realign them into the neutral position, align the shift rod so that the actuater in the shift cover is also in the neutral position and then go through the adjustment procedure for the cable and linkages that go to the T-handle shifter.  This is all assuming I don't have something like a broken shifter fork or worse inside the transmission. 

Any tips/advice or things to look out for would be a huge help at this point and I will relay it on to him.  Also, were there any updates for this kind of problem?  I remember seeing something about grinding a slight chambfer on the gears to help with shifting in the bulliten about the updated transmission brake and other improvements for shiftability, but I'm not sure I feel comfortable grinding away the collar teeth of my tractor's gears... 

Hurst