Do the original valves need replacement? If you need to bump compression a little bit then mill the heads or run a thinner head gasket. Seems like a lot of expense for little gain.

I see you're looking at custom built headers too. I haven't read the entire thread, but you might want to think about adapting one of the new eight speed transmissions. Expensive, but a lot to be gained from it. There are controller setups to shift it manually.