This is awesome, seriously.
Given that it's a logish manifold i don't think a relatively minor port mismatch is much of an issue, if it's even an issue at all. Especially if the ports have been ground on to match up better.
If you can use a full width radiator i would, just because an aluminum half width, even with a double core rather then the stock 1.5 core, cools a bit less then half as efficiently as the stock one. It's enough to keep things under control as long as you aren't doing sustained boost runs, like high speed or especially track driving.
As to the exhaust valve, speaking from a very generic standpoint if it has started recessing itself into the seat, or the seat has started sinking into the head, you're headed for trouble. If you're lucky it's just been ground too many times and won't close up the lash any more then it already has, but i wouldn't bet on it. Given that you obviously don't mind treating this car like a racecar (put it together, take it apart, put it together, take it apart, put it together, drive it, take it apart, etc.) too much, you might as well slap it on and see if it stays together or not, worse likely case is that it closes up it's lash and then burns. Absolute worst case is that it's stretching and the head snaps off, but i've only seen that on one (1) honda, ever, out of hundreds of them. That said, it made one hell of a mess.
Anyway, i think this whole thing is awesome, keep up the good work! Ignore the naysayers and the haters.
Considering the amount of power you ought to be making at 16psi, i think 50k miles is pretty damn good.