Perhaps I should clarify myself - the Bisson muffler indeed fits very well inside, with just a little clearance needed for the low point, as Bob and Tom (Hey, sounds like radio personalities!) pointed out. I had it cut very similar to Bob's at first, and looked great!

I will be using several engines on the Giles. One of the others is an A&M 4.2, with, I believe, a Sonic Pitts (don't quote me!), that hangs significantly lower, by my calculations - the larger hole allows for that, as well.

I'm not recommending my cutout, for the ZDZ80 with Bisson, just illustrating what I did. My cutout will just make it easier to change engines easily, without having to modify each time.

Ran into that with an Extra I bought used - by using a different engine, I found that the cutouts the previous owner had used, didn't work, and when I was done, looked a lot worse than had I done it like the Giles...