I have a 2N that has a worn out linkage. If I am careful to move the lever to neutral before moving the lever left or right it never gives me a problem. If I get in a hurry and apply side pressure to the lever before it reaches neutral, it will sometimes leave the last gear engaged while engaging the new gear, resulting in the lockup you describe.
When my tractor does this, I remove the transmission filler cap and look inside. Both shift rails will be engaged in a gear. I think mine always has one to the front and one to the rear.
Make sure the shift lever is engaged in the slot of one rail, then use a long screwdriver or prybar to return the other rail to the center (neutral) position. You will have to unload the gears by taking the PTO out of gear and rocking the rear tires while you do this. Sometimes holding the clutch down helps, but most of the resistance comes from the output shaft end.
I have never had to jack up the rear wheel to get mine unstuck, so try rocking first.