What is the ms3's piston to valve clearence?
Stock ls6 heads.

 

You'll have plenty on the stock head.

 

How about on aftermarket heads (AFR,ETP)?
Do plan on doing heads later on.. Not sure if aftermarket or if I should just get my stock ls6 heads massaged...

 

You'll have plenty on any of those heads. Once you start milling them and/or changing the thickness of the head gasket is when you'll need to start measuring PtV.

 

i would not say plenty anytime your doin a cam that big you should check pv. I am in the process of puttin darts on my ms3 and the valves are hitting i just sent them back to tsp bc they are not much smaller the stock heads so they should clear.