Went home during lunch, and verified my previous measurements...
You'll have to bear with this, my father is the mechanic, I'm merely a noob who enjoys milling:
placed the straight edge on the gpu gently. Took out his feeler gauges that he uses for checking heads for flush-ness. Switched to the largest available feeler. I was able to slide this under both sides of the straight edge. The gpu is not flat, and it is certainly convex.
If its worth polishing cpu blocks til they are mirror like, why would i settle for only 1/16 of the top of the waterblock to contact with my gpu? I don't think its an option to reshape the gpu block. The chances of me getting them to mate good is just about nil, and there isn't a whole lot of material left on the bottom (made the bottom plate as thin as I thought was reasonable.)
I have always been told that very minute scratches on a cpu block reduce performance... I can't imagine a 1/32nd gap is acceptable
So... Does anyone know how much material I have to play with?