Ok so last night I couldn't work outside on the manifold I'm busy building, I don;t work on them inside since the grinding dust gets in everywhere, and decide it was a good time to tackle the "new" gearbox.
The only thing immediately wrong with the new box was the selector arm in the extension housing that has had it's bush completely destroyed over years of driving it and not fixing it. So the gearbox had to be opened up to do this unfortunately, but I've opened them so many times by now it's very easy and quick to do.

I then realised that the "new" box has a slightly shorter gear lever extention housing than the old one, so I had to swap the arm and gearlever housing over. New box with longer gearlever extention housing already swapped on the left and old shorter one on the right.

New gearbox with the bell housing and lever housing swapped over on the left and old one with 21R bell on the right.

"New" gearbox still looks good on the outside, I just gave it a quick clean so I can work on it and not get completely covered in old engine oil and grime. When I opened it up I decided to open the front half as well, just to see what the synchro's look like and all I can say is I'm as happy as a pig in #OOPS#. This gearbox is so smooth and the synchro's look like they came out the factory yesterday. The only thing I'm going to do is to replace the front and back seals to make sure it doesn't leak any oil. Not that it did, but while it's out...

EDIT: The gearbox came out of a Cressida station wagon btw...