You may be better off contacting these people.
http://www.trocltd.com/intro.html
However just from what I found on the computer and the size of the engine, I don't think the Triumph's bay is long enough to house the length of the Jag engine.
The Jag engine will also be much heavier, so there's that to think about.
Maybe a modern V6 or a modern 4 out of a Miata _ just throwing some ideas out there...
Personally I would just restore the original 4 cylinder.
The other problem you face too is if you put an engine in there with more horse power, will the rear end take it.