Had one for 10+ years, great car when restored, lots of fun to drive and rarer than almost any car on the road that you could drive. See mine at http://www.v8triumph.com
Parts dealers - Rimmer Bros in England http://www.rimmerbros.co.uk/
Club - Stag Club of America
http://www.triumphstagclubusa.org/
Engines are fragile, engine swaps can be done but upset the balance of the car if they are too heavy. Believe it or not, the rover V8's are too light and make the car float at speed. A Ford or Chevy V8 with aluminum heads would work but need to upgrade the rear end to handle the power. Transmission and rear end are very similar to a TR6 (upgraded with larger bearings, etc..)
Good luck, thought about getting another a few times, but so many cars and so little time!