LooneyTunes

The 91/120 size DP Ultimate was reviewed in the Dec. 2001 issue of Flying Models magazine. They installed a YS 140 in the test model. I've enclosed a look at how they routed the muffler
The parts are also available for the YS 53 which I assume will also fit the 63. You can check them out at

http://macspro.brinkster.net/four_parts.asp

I'd like to install a pitts style muffler on mine but I can't find one for the 63 so I plan to follow the Flying Models example to keep the clean look. Hope this helps.