I have to agree Charlie, if bolting on the stock Mazda exhaust manifold gives some of the best sound reduction at 15 lbs that is not a bad idea.  It looks like a best-fit for pusher aircraft (aimed in the right direction) but I think it just might work for some tractor configurations as well.  I threw my exhaust manifold out during my engine conversion, opting for headers with the expectations of best horsepower and reduced weight; not sure if I got either; would be an interesting experiment to swap from what I have to that simplified and very solid install.
Jeff

Looks, in concept, very similar to what Ed Anderson tried many years ago with split-washers-on-allthread. Would be interesting to know what it costs in power, & what it actually does to the exhaust. It *should* strip off the high frequency energy, which is the biggest battle for the rotary. Gotta wonder about power loss, though. It's amazing what a good job Mazda did with manifolds on the old 13Bs in the cars. Paul Conner's SQ2000 was the quietest rotary (or at least the least offensive) that I'd ever heard, until hearing Dennis Haverlah's Renesis.
Attached is a pic of Paul's installation. It sounded almost like a small block V8; very pleasing. And the total weight (~15 lbs) probably isn't any worse than most of the custom stuff we come up with today.

Charlie