I'm guessing these are almost identical to the little XLs and Super 2s. They have a single long screw that attaches them to the engine. Have you removed the mufflers? If so, a little heat is good to burn any gunk that may be acting as a glue holding the muffler halves together. I use a propane torch to clean mufflers all the time (removed from the engine of course!). It should be evident where the halves of the muffler join. I'd heat around the perimeter, then tap with a hammer (not hard enough to dent it, but enough to jar it free).
Good luck,
Dan