So I went to check out a Black 2007 z06 today. Nice car. American import, with cam headers and exhaust. From the bills the guy had it looks like the valve train has all been replaced, but it doesn't say anything about have the guides replaced. The work was done by SPI tuning. We went for a drive and it ran strong, but there was a definite ticking from the engine. Red flags went up in my head. I think I'll have to pass on this one.