Hi from the U.S. I just joined this site as I'm considering a Mk1 V6 conversion project using a Ford 2.8 liter Cologne V6 engine:
http://en.wikipedia.org/wiki/Ford_Cologne_V6_engine
This is a popular engine conversion amongst Sunbeam Alpine owners in the U.S. as the 2.8 V6 is cheap and can be tuned for reliable, tractable power. Not as much grin factor as a V8, but a lot less hassle to fabricate, and fewer cooling issues to resolve. It seems like this would be a good choice for a Cortina as well, mated to a T-5 transmission and an 8-inch rear end.
Has anyone done a conversion using this family of Ford V6's? I couldn't find anything searching the forum.