That Toro looks a lot like a Kawasaki 26.3 cc engine that I have converted.The intake on your looks a lot like the intake on mine, and the casting on the front of your crankcase looks a lot like mine before I cut my crankcase. I found that the heat dam from a Stihl 25cc engine would work on the Kawasaki. I used the stock muffler but I modified it a little bit. There is a picture of my Kawasaki in this thread.
http://www.rcuniverse.com/forum/m_25...tm.htm#2525185