I would make sure you have 1/8" gap between muffler and fuselage so it doesn't hit from vibration.

The muffler sticks down pretty low. It looks like you could take it off and just use the header pipe. If your field rules permit this, you should give it a try. The motor sounds real nice and is not too loud without the muffler. I run mine with a short piece of Al tubing over the header.

You can post a second picture my replying to your own message.

Tom