The 455 SD is a classic example of why you don't gain a ton of power when you increase compression ratios a full point. As you say, moving air is another way to increase power, over raising compression. Moving more air doesn't have the possible drawbacks that increasing compression over your fuels ability to supress detonation does. More naturally aspirated air doesn't break pistons, or rings.
As I previously posted, on a late 2nd gen T/A I would go for full length headers over RA manifolds, because they have the ability to move more air. If you keep the low compression, you have to move more air to compensate.
I had a customer that actually managed to order a 73 SD 4 speed car, removed the RA manifolds and substituted Hooker super comp headers. The car noticably picked up with just that modification. No times, just butt meter readings.
Another customer car, 1976 455 T/A, cam, headers, H pipe, intake. it ran a 13.92 with 7.6 to 1, 455 D port engine, basically the same engine that came in a B body daily driver. The car would run out of gas just before shifted, due to the stock fuel lines. Probably would have run 2-3 tenths quicker without fuel delivery problems.
During the late 70s, early 80s, there was no premium pump gas, if you wanted a quick street car, you had to stay with low compression for the low octane fuel available.
During this time there were tons of older high compression factory heads available, cheap too. If you bolted GTO heads on your late smogger T/A you couldn't get fuel for it. At this time all the premium fuel engines left over from the late 60s were blowing up due to broken pistons, and rings. I wasted a good 65 Bonneville 389 this way.
