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I would not change the compression ratio. Going with more duration will add power but do remember that the rpm power band (should) move upwards.

I'm not so sure the money spent on "Big Mouth" heads would be worth it. Here's why. For the money spent, you will be maxing out the stock replacement heads ability. While I do believe there will be a gain, for the money spent the gain is small.
I assume you know all of your heads flow numbers at all lifts as a comparable list against the Big Mouths.

My point is, perhaps a better head like a Indy or Victor head may be in order. Pricey! But a much better platform and higher ceiling.

Do your homework and take note of how the heads flow at all levels.