I only had the ZDZ-80 for a few test flights, and I thought I remembered that it fit entirely within the cowl. I went back and looked at some photos but there is nothing definitive.
I don't remember having to make a cut that large, but I have mounted and tested so many engines I get lost on what's what.

The 3w75 front carb with johnson wraparound muffler DOES fit with the muffler entirely enclosed, maybe that's what I was thinking about.