The problem is that I had a lunched overdrive on my scimitar. I removed the gearbox and overdrive in one and then attempted to remove the overdrive so I could fit the rather expensive recon unit.
This car has a LH overdrive, as featured on some MG's. On all the MG websites I found info on they said to not take the adapter plate off the gearbox. I asked for help on a Scimitar website and was told by someone who had done the job before to split OD and adapter plate as one, from the gearbox. This turns out to be bad advice from someone who was, I think, intending to strip down their gearbox for inspection anyway. He has since crawled back underneath his rock and won't reply to my emails so I am stuck on the other side of the world (i emigrated and took my car with me) with a gearbox that won't go back together.
So for now my quest is.....
Make the adapter plate go back on the gearbox so I can fit the OD and get it back on the car.
Here is the whole lot (not my gearbox) so you know what I am talking about. The thing with the yellow arrow pointing at it is the adapter plate

In my struggle to remove the overdrive, the shaft below and the big cog thing at the base of it came out of the gearbox. I managed to get the cog bit under the bearing you see in the pic to go back in but it is still not in properly, I think. The reason I think this is that when I put the adapter plate back on and tighten the 4 bolts it clamps the shaft so it won't move. Also the whole lot is stuck in reverse (but i think this might be related to it sitting on it's end rather being in the normal horizontal position (i need to check next time I am in the garage) which may or may not be related.

So this above picture is my gearbox. You can see the hole on the outside of the bearing at the 9:30 position. The adapter plate has a pin that sits in that; that was in place when I tried to replace the adapter plate.
Why won't the adapter plate go on? What have I done (if anything) and how do I fix it?
Thanks
Stephen