ORIGINAL: Mr67Stang
I had this plane and flew it with an OS .50sx and used the bolts from the stock muffler for the Pitts muffler and had no problems.
Were the bolts from the .50SX a bit longer?
If I recall correctly ( it's been a while since I put it together ) the stock bolts on the .46 were about 1/4" too short for the Pitts Muffler.