I run a very tuned, fast road TR6, and read this thread with interest.
If the engine is assembled well, and very carefully balanced, with a good cooling system and very frequent oil changes, the engines and very robust, smooth and powerful, and will last.
I used a ribbed block from a saloon, and I am on a +40 bore, with AE pistons, late TR6 crank, Carrillo rods, Newman cam, Newman steel followers, lightweight steel flywheel, ARP head bolts, line bored, and has not given me a single issue since it was built in 2011, after X2 Round Britain Reliability Events, X3 10 Country events, trip to Le Mans, Sprints and hill climbs, track days, and driven regularly to 6500+RPM based on an electronic (Stack), accurate tachometer. 40-50k miles. I just run a regular crank damper, and had no issues in the department either.
Vibration free balanced the below components:
AP Racing Clutch cover.
Lightweight steel Flywheel
Not a cheap undertaking, but well worth the effort.
Some good advice above, and read with interest !