I would think, that on a low red line rpm mild 455, 5200rpm, that port matching would be enough! That's all I did when I put the 400 heads on. With a cliff spec qjet, blowing through stock logs, it's still pulling hard at 5200rpm! Never turned it any more than that.
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 1970 amc rebel 4-door, faded blue paint,290 emblems on car, 455 under the hood.Turbo 400,3.15 gear.
Best so far 1/8 et,8.90 on street tires,
Since that I have added 400 heads.
I call it a rat sleeper.
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