2 Guys 3 hrs and still not in. lol
Ahh the joys of a manual tunnel!

It is a bitch hey. On mine I jacked up the front of the engine until I could get a better angle on the gearbox.
One thing Dattodude pointed out to me once when he was telling me about how fit a gearbox on a CA18 in a 1200 was to undo the crossmember bolts and lower everything.
This should work on your car too.

One other thing, when you checked that the clutch you got off the other engine was the same, did you check that the splines on the clutch plate mesh with the gearbox splines? I am sure you would have.

But really it is a pain in the arse to fit with that tunnel, you should be lineing the box up then pushing it forwards, but it sounds to me like you are just going to far forwards and then the input shaft is getting caught on the clutch pressure plate. Just take your time and line it up then push and if its not going , bring it back move it a bit to the side or up and down then push forwards again.

3 hrs lol.