In preparation for Okteenerfest, I finally resealed one of my leaking gearboxes and planned to get it installed this weekend. Was having difficulty mating it to the engine so pulled it back out and found I cannot turn it by hand when in gear - I tried them all. In neutral, I can turn the stub axles in opposite directions and hear the gears moving and the shaft does not spin.
On the gearbox I took out, I can rotate the stub axles and the shaft spins (guessing it is in gear but not 100% sure). Can't easily change gears on it since I removed the shift console to use on the resealed unit.
When I resealed the 'box, I removed the stack to change the shaft seal. Put everything back in and didn't have any leftover parts Even watched Dr Evil's video.

Any ideas on what might be going on?

UPDATE: I removed the nose cone and everything moves as it should in/out of gear. But when I replace the nose cone... it binds.

What should I look for? I have removed/replaced nose cones before without issue.

If I recall there is a spacer / thrust washer that can cause jamming of 1st and reverse if not installed in correct orientation?

You are correct! I had the flat bearing on the wrong end

Thanks for the suggestion. I figured that's what it was when I removed the nose cone from an extra gearbox and saw the order. Just got things swapped and works as it should. Gearbox is mated to the engine.

Good job!