Hey if you want, my transmission is literally sitting on the floor in front of my toolbox. Space is at a premium right now, but if you give me a couple days I can get a bunch of pictures of it for you to compare to. I'm fairy positive that in the USA, the Capri was only ever sold with a Mercury badge. The fact that you have no XR2 markings on the car might mean that it was a base model, but then again yours has a turbo. What was on there before you put the big boy on? If it was the IHI turbo, I'm pretty sure that's the factory one that came on the XR2's. Is it possible the previous owner had done a turbo swap on a base model Capri?
If you need me to open up the gearbox and count teeth on the 5th gear, let me know. Somewhere in that post you linked, I think I saw tooth counts. The only way you'll know for sure what you have is to open it up and look, I think.
Edit:
Holy crap! Does that page say that gear swap will give this thing a 165mph top speed?
Really?