Indeed... A .030 mill with the PermaTorque head gasket is going to yield a 10.1:1 compression ratio, and put dynamic compression and intake closing right on target with a 10:1 340 with ‘68 four speed cam. The low lift flows of those heads are still very good, which shows an efficient port layout and design, so the low velocity isn’t going to be as great of a concern as initially suspected. But, it will need to use 1.5:1 rockers. I had originally stated 1.6, and while the extra lift wouldn’t hurt anything (except probably valve train geometry), the extra duration added in the .050–.200 lift range (even though it doesn’t effect the seat to seat duration) would cause a drop in low rpm cylinder pressure and torque. 10.1:1 comes right in with a DCR of 8.3:1 and a cranking compression of 160 psi. While this is probably beyond what a set of J heads would tolerate, the closed chamber heads with the .038 quench will work well enough to allow good static timing and something close to a performance mechanical advance rate.
Yeah, I'd run that valve train and not lose any sleep at night over it... Everything else looking great, too!
