What kind of trouble did you have with the hardened valve seats. I'm rebuilding my '63 TR4 and maybe I can avoid any trouble.
What would you have done different?
I don't really know what the problem was; but I think my mistake was using "racing" valve springs and not checking the seat pressure. Or it might have been the too-high compression ratio and not removing the sharp edges in the combustion chamber. Or even the MMT-based octane improver I used to compensate for the high compression ratio and tendency to knock. Another possibility is that the altered combustion chamber shape (from milling the head) was enough to move the mixture lean during high rpm medium throttle operation.
At any rate, those are all things that I will do differently next time. I probably should have tried running lead substitute to see if that would stop the recession, but I didn't. (I was kind of distracted with other things at the time and driving the TR was a sort of therapy to keep me going.)
Here's a shot of the modified head, after perhaps 20k miles of mostly street driving:
As you can see, the exhaust valve has extreme recession. It was so bad that I could no longer adjust the valve lash, even with shims under the rocker pedestals and shorter pushrods. The spring retainer was literally hitting against the rocker arm! Less obvious, the intake valve seat (which is still the original cast seat) has recessed a bit as well. At the time, I just threw the modified head in the corner (where it still resides) and installed an unmodified head from another motor (no other changes). It was still running fine (though not nearly as much torque & power as the high compression produced) a few years later when the car got totaled in an accident.