dbane261,
Sinking the intake seats by an amount equal to the thickness removed from the head has been standard practice for the stovebolt six heads to maintain valve-to-piston clearance. This was described in the May 1955 HRM article. I would not to mill the head by as much as 0.100". Work through one of the online compression ratio calculators to see what the difference in the gain in CR is for 0.060" and 0.100" of milling the head.
Did Clifford offer any dyno or road test data to support his claims? We have a saying at where I work about performance claims that seem almost too good to be true: Trust but verify!
Clifford equipment was not around when I was running 235s and 261s. My stuff came from McGurk and Toros.
