I just got a set of 906 casting vortec heads. Do I need to have them machined to fit springs that will take my lift? Or can I just put in springs that are the same diameter? Also, should i change valves and rockers and all that or are stock ones good enough?

What kind of lift are you going to run, and what spring were you wanting to use?

.488 lift and I don't care what springs, as long as they work.

with that kind of lift, the stock vortec springs wont be adequate, you should get some comp 981s , if i recall corectly, they are 1.25 diameter spring, the same as the stock vortecs, also you may have to have the valve guides milled down

kevin