My experience with running '65 and '66 389s: all the '77' and '093' heads are GTO heads and big car 421 heads, regardless of intake system. There is no difference in the head between tripower and 4bbl application. Only in the intake and camshaft. No block differences except for the stamped number. All of the '77' and '093' heads I've owned were double valve spring heads. I have been told by more than one machinist that hardened seats were only preferred on Pontiacs (which had/have pretty hard seats to begin with...much harder than Chevy or Ford) on vehicles that were under constant high load conditions, such as pulling a trailer or sustained high speeds above 3000 rpm....more like 3500 and up. I did not install hardened seats in my '77' heads on my '65 GTO when I had them done in 1981, and that was 33 years and 50,000 hard miles ago. No problems with them still. And I'm running a pretty big cam in that car, too. So, hardened (unleaded spec) seats are preferred if you are towing a boat, car, etc, or are buzzing cross country at 3500 rpm with a 3.90 rear gear. Otherwise, IME, not really necessary.
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Jeff 
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