Carellh has the best idea,welding alum. is a art.a TIG welder is a special type of machine for welding somone who repairs aluminum parts would have one.
without a photo of what you were talking about there was alot of missunderstanding about what you were asking, the link you provided was for the new YS engine, with the new style muffler, with jamb nuts, and a screw on muffler hence the confusion.if you have a small tap drill a couple of holes in the lip and thread some small machine screws in there.
the JB weld says its good to go for aluminum, the stuff is pretty strong and rated to 600oF you might not even need screws .