I know you can get a pitts for the DLE 20 from http://www.jtecrc.com/DLEpittsstylemufflers.htmthere is also a wrap around style that will bring the muffler right behind the engine below the carb. and you may want to get the engine from my understanding going with a gasser on the smaller planes weren't designed to fit so you may have to recess or even move the firewall back a little to get the proper fit.
Jordan