I wouldn't lathe the ribs out... You're just turning it into a wider but shallower V belt that way and you're not going to shed more than a couple ounces. I don't like undampened harmonic balancers, but you can get them in aluminum, shed a significant amount of weight and still keep the extra surface area and migration protection (a pretty healthy choice if it's running right next to your timing belt... x10 if it's an interference engine). Keep in mind that while you can run a higher tension the retaining wall is 1/3 as tall; Removing the ribs which help prevent the belt from migrating or jumping may make it even easier to throw the belt than if you just stuck with the V AND you're losing surface area for the belt to grip.
Other than that it sounds cool and I hope to see more.
I'm going to move these past couple posts to a new thread for you in the Off Topic section so they don't pollute this ad. I encourage you to post more... I'd love to see some pics.
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