1976 Cortina - from 4 speed borg warner to T5?

[wolverinedo]

Hello! Another new member here looking for the answers to the many problems I've created for myself! ie Why didn't I just buy a new car?!?

So I'm wondering who out there has done this before or just knows how it can be done:

I have a 76 TD cortina, came out of the factory with the 250 six (not crossflow) and the 3 speed auto.
It now has a steel headed 250 crossflow out of an XD (i think) which is nice and warm and putting out around a lazy 120kw @ the rear wheels, and we've also swapped the auto for the 4 speed borg warner manual box.
Basically the borgy sucks and its time to throw it out for new and improved! Obviously the T5 (out of the XF and later falcons) 5 speed would be super sweet, but what we don't know is how much needs to be changed/modified to get it in. I have had an opinion that it will slot straight in to my current setup with only the gearbox mount needing to have an extension welded on. Sounds WAAY too easy!
My other option would be to get a 4 speed toploader which came from the factory in some TDs and while not giving me that glorious 5th gear at least they are a nice strong box that can handle some abuse.

Any opinions or knowledge from you guys would help here - even suggestions as to who/where I might get some help from. Im in Adelaide.

Secondly but as importantly (since I've left it so long its now summer and she's hating the heat!) cooling the ol girl. It originally had the engine fan plus stock radiator (2 row I think, about 7 years old and half blocked!), but last year I had the engine fan tossed to make room for a 12inch Davies Craig fan (mounted inside, sucking air through) mounted on the stock radiator. Its fine in every scenario except sitting in traffic when the temperature is over 30 degrees.
So unfortunately there is no more room inside to put a bigger diameter fan to suck through, there is just enough room to install a 10 inch fan on the outside to push air through the rad, and of course the radiator itself is old and shitty.
Suggestions? Obviously replace the rad is first priority but do I go for a recon-factory rad or a thicker 3 core? If I do get a thicker rad I won't have room for a fan on the inside at all (so little room between the end of the engine and radiator)... So ideas please!

Thanks for your time gents, I do look forward to reading what you have to say.

Best regards