the problem I see with the moki135 and probably the ST is silencing. My moki135 on a bcm pitts silencer is considered too noisy for my field with a standard 82db limit. I havnt measured it but I am confident its over 82db. You can buy an Aviation Alloys silencer from Just Engines which gets the noise down to a legal limit, but the silencer is massive and I doubt it would wont fit in the cowl.

Maybe if youre going down the big 2 stroke route with the Capiche 140 a pipe is the answer. Can you get throttle pipes for engines that size ?