I had a TR7 into which I fitted a Dolomite Sprint engine and uprated brakes. The conversion is relatively cheap, quite straight forward but produces dramatic results. The 16v engine is really smooth, torquey and surprisingly powerful - and far cheaper to run than a V8. I gave it electronic ignition and a tubular exhaust manifold (needed to clear the chassis leg) and my mate's professionally converted TR7 V8 could not get away from it.
One of the classic car mags recently put several Triumphs on a rolling road to see how they fared - a totally original Dolomite sprint with no mods at all was pushing out 140bhp. Bear in mind that this is from a 1970s engine with twin SU carbs and mechanical (points) ignition system and those figures start to look very good indeed. 140bhp is more power than factory spec MGB V8s or TR8s had, by the way.