How much can I mill the head without having valve clearance problems? Using 91 octane fuel on the street in a TPI equipped S10 Blazer weighing 4000 lbs...max rpm 4500...cruise 2500 rpm...stock hydraulic roller cam and lifters. Or would I have better luck changing pistons to get compression back. I would like to keep as much jingle in my pocket as possible.

Are below figures correct:

350 L-98 Stock 4.0 dished piston

Head chamber vol. 65.2 cc = 8.71CR head mill=0
Head chamber vol. 64.2 cc = 8.82CR head mill=.006
Head chamber vol. 63.2 cc = 8.93CR head mill=.012
Head chamber vol. 62.2 cc = 9.04CR head mill=.018
Head chamber vol. 61.2 cc = 9.15CR head mill=.024
Head chamber vol. 60.2 cc = 9.27CR head mill=.030

Piston Dish + valve Pockets = 10.0 cc
Piston Deck = -.025" = 5.148 cc
Gasket compressed = .038" = 1.95624 cc