If the stock bores were that bad then the stock OEM motors would never pass an emissions test. (blowby and oil contamination would give huge unburned hydrocarbons) They tend to pass strict emissions tests so the ring seal quality must be pretty good.
Check/measure the dish volume of your pistons. (its not that hard to do) If they are -12 to -15cc mill your vortec heads .040" and install with with the .015" shim gasket. the stock 350 pistons should be .025" below deck @ TDC or close to it.
Your cr will be between 9.6 and 9.8:1 finished with a 58-60cc head volume.
Thats plenty enough compression for a street motor.
GM doesn't recomend flat milling more than .040" off the deck of these heads.
The physical flat mill limit is the stock intake valve seat edge.
You'll be fine at .040".
About the only way to keep it low buck.
Last edited by F-BIRD'88; 05-31-2008 at 11:44 AM.