The "Hemi"6 head isn't actually a hemi, it was just called that for marketing purposes.
As for the flat tappet style cam blanks, there is only material cast on the lobes to accommodate grinds in the conventional valve layout, when you change the valve layout, an intake lobe becomes an exhaust lobe and vice versa based on the original OEM valve layout, so you will end up with lobes that have material in the wrong orientation or not enough material to make the lobe. A billet roller cam has a full round lobe and you won't have that problem.
There are at least 3 better cylinder head solutions than even considering a hybrid head, and all 3 will likely outperform a hybrid head and be much less expensive and won't require any custom parts.
50 years ago, there may have been a reason to create a hybrid head for some engines(like the Ford 240/300 6 cylinder with 351C hybrid heads) because the OEM heads may have not been able to exceed the capability of higher performance heads from other engines. That's why you don't see it done today, in the case of these Chevy 6's, there are better options that make a hybrid head unnecessary, even for the most extreme HP levels.
