The chamber diameter is roughly 4.250........ At .080 that works out to about 18.6cc worth of milling.

Installing larger valves, along with using valves with flatter heads reduces chamber volume.

67 + 18.6 = 85.6cc.

I can see that as a starting point with oversized aftermarket valves.

The outer row of head bolt bosses are a nominal 1.00" thick, stock.
If you measure a few it should give you an idea how close to that .080" has been cut off the decks.

This is why you measure instead of assume.
They are what they are.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads