Missed on this combo?

Very interesting, IM. Reminds of the troubles with 351C exhaust posts.... narrowed down over a huge shortside hump then opened way up and formed a low velocity area before the exhaust flange. Guys did all sorts of things to fill that low flow area to keep the velocity more uniform throughout the ex. port, which helped the whole exhaust system work quite a bit better; epoxy was one of them. It'll be good to see what you end up with; I'll hand it to you for being determined to make this work

What kind of guns?