Look in the OS parts list on Tower. Often you will find that muffler extensions have the same number for different engines. I bought a muffler extension for a .46 LA that also fits other .46 size engines. If you find a match look up the Pitts style muffler lists for all the engines that can use a matching muffler extension. Perhaps a .46 SX or FX will have a muffler listed that is not listed for the LA. Failing that find a friend that has an SX or FX and try his muffler on your LA. If it will fit without alteration just get a Pitts for that engine.