Originally Posted by Truckracer

Oh MY!!!! You have way more of a problem there than just the muffler fit! That is the standard side exhaust DLE55 engine that someone has turned the cylinder 90 degrees so the exhaust points to the rear. That simply will not work as the piston / cylinder assembly is not designed to work that way. If there has not been any internal damage, you could just turn the cylinder back to the side exhaust configuration and run it that way. If it has been run at all in that configuration, I suspect the piston and cylinder might be junk now.

The side exhaust 55 and rear exhaust 55 are completely different engines and very few parts interchange between them.