Part of me feels that if I'm going to throw 10/15/20k at the car to build the ultimate engine, I'd rather spend that money on another period car that's more capable in the first place, something like an RS2000 or Sunbeam.
Or a 6R4?
Good luck on finding a 6R4 for £20k.
We must have been lucky then with the one we picked up a few years back.