I used this expanding foam called "Great stuff" and I've been carving it out with an exacto knife and an orbital sander. I think it looks decent so far. I didn't want it to look M3 because, well, it isn't. So I went with accentuating the stock lines and giving the lip an M6 (new M6) look.

Thoughts? I'm kind of at a loss as how to blend it in with the stock molding. it looks kind of off down there.