Originally Posted by MouseFink
The V6/V8 Vortec heads have valve spring pockets that are thinner than older heads. I would avoid cutting those seats any amount and make up the difference with longer valves. Machine Vortec spring pocket depth at you own risk.
Your set up may vary but my 4.3L V6 engine as-built spec. would be a good guideline:
Used Manley 1.94" #11860-1 int. and 1.600" #11863-1 exh. valves x 4.951" long, 11/32" stems, with a .290" tip length for extra .020" clearance (total of .040") between the locks and the self-aligning roller rocker arm rails. Stock Vortec valves have .289" tips.
Used standard Comp Cam 613 locks on the exhaust valves and 614 + .050" locks on the intake valves.
Used Alex's Parts 1.255" OD x .875" ID shims to achieve 1.750" +/- .010" assembled height for 144 lb. seat pressure. Different shim stacks were required on the exh. and int. seats after eliminating the exhaust valve rotators.
Used a Comp Cams #4721 seat cutter to enlarge the spring pockets to 1.350" OD seat x 0.775" OD spring locator boss to fit 1.310" OD x .885" ID Comp Cams #26918 beehive valve springs.
Used Comp Cams #4726 guide cutter to cut intake and exhaust valve guide from .562" OD to .530" OD to fit Comp Cams 518 Viton .530" ID x .575" OD seals.
Reduced valve guide height by .200" with fitted .060" between the Viton seal and the lower spring locator boss. .
I take it you get your valve train parts for free? Obviously cost isn't a concern.