It is a bit hard to answer in text, yes I had to cut the cowl a bit - mainly to allow the muffler to poke through.
It is better describe with a pic, have a look at the pic about half way down, and also how the 120-ax mounts and the next page.
http://www.rcuniverse.com/forum/m_47..._7/key_/tm.htm
cheers
- Kevin