hi lou  i have a current model fox 40 bb abc engine and used one of my brodak 40 tongue mufflers made by  big art which i brought from virginia hobbysport. bolt holes need some fileing on muffler  to line up but when bolted up look made for it .
hope this helps damien

Thanks, guys,

That's a good start!

I'd considered the alternative of making up a 1/4" thick adaptor, threaded for an available tongue muffler just outside the flush-sunk heads of the 6-32 oem mount bolts.

Any shape or flow transition can be made in such an adaptor...