This is a great looking plane for sure - has gone to the top of my shopping list for next years plane -- am eager to see reviews of those who get now. Am not really into 3d, but love tossing a plane around anyhow - so a sport aaerobat this seems to be.
Also wondering about muffler, and found if you check out the build manual for it - pg. 17 ==
"If you installed a two-stroke engine, attach a Pitts-style in-cowl muffler. The stock muffler could also be used,
but excessive cutting of the cowl would be necessary. We suggest using a Pitts-style muffler as shown in the picture."