That sounds good. The trick will be fixturing it. Others do it. They may use a jig on a belt sander. Headers by Ed used to do it. Calvin Elston and all of the custom builders do too. This evening I can search on Speedtalk forum - I know it came up in discussions.
I kindof hesitated to post these here, but this what I found.
I did the best I could using a glass plate and sand cloth, but the overall arch was more than I could address. I wasn't terribly concerned using the fat gaskets and such a thick flange.
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