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For a daily driver, a 455 engine and a stock Q-jet manifold is obviously the best choice, if you can find a 455 engine that is still rebuildable. Good 455 Pontiac engines and cranks are becoming difficult to find but they can be found with some diligent searching. The drag racing crowd has grabbed those engines. Do not use 1965-1970 heads on a 455 CI engine if you want to use pump gas. Any of the 1972-1979 Pontiac heads will produce a compression ratio that will work well with 93 octane pump gas and will still make good torque and horsepower up to 4000 RPM.

Option #2. Step down to a 389/400 engine if a good 455 cannot be located but be advised, it is difficult to use production Pontiac heads on 389/400 engines. The 1967-1979 Pontiac heads that are available will either have too high compression for pump gas or too low compression ratio for good power. The best option with a 389/400 engine is to use 1967-1979 heads with factory screw-in rocker studs with hypereutectic dished pistons. The 1965-1966 heads will work but are kinda "left-handed" heads since they have small valves and pressed-in rocker studs and should be left for the restorers.

Do not use a 326 or 350 CI Pontiac engine under any circumstances. .

The only thing that will make more horsepower and torque than cubic inches is rectangular money.

 

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A 455 short block , any reasonably priced 1972 - 1979 cast iron heads you can find that are still in rebuildable condition, Summit K2800 hydraulic lifter camshaft, Edelbrock 2156 Performer intake w/o EGR, Rochester Q-jet , Pertronix D1200 Street/Strip HEI distributor and a well built TH400 is the only way to go for a part-timer using pump gas.

You will not regret it.

 

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On the subject of later model cylinder heads for my 389 build I was told the 6S (9) High Performance (AIR) heads were designed to reduce smog. How they did this I'm not sure. Should these heads be avoided? They have the right chamber size for my app (93.74cc), they have the large valves, and they use screw-in rocker studs. Sounds pretty good to me. Matches the specs for a pair of 6X-4 heads, no?

All 1955-1966 Pontiac heads have 68 CC combustion chambers, pressed in rocker studs, small valves and the valve seats cannot be enlarged to accept large Pontiac valves. The 1955-1964 intake manifolds will not fit the bolt pattern on 1965-1979 heads.

 

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There is not a dimes worth of difference in any pair of Pontiac heads made after 1971.