Artificer, I admire your ingenuity. Any man who will take on a bias-cut tailoring project is brave, indeed. Sometimes, the less talented craftsmen of the world (which surely includes me) must resort to shims to make things work that might not otherwise- not that I would stoop to wood filler... much.

But I have this suggestion that might make your vest project a little easier- consider facing the lapels in black. That gives you a little less matching and geometry to deal with and it would be completely appropriate for a formal vest (IMHO).

Send us some pictures when you have finished.