On fitting mufflers to the pipes you have they make sets of adapters. A lot of mufflers come with them. A series of short sections of pipe that fit inside one another and you fit one in the muffler, the next size one inside that, keep adding till the piupe fits. If the muffler has a 1 3/4 inch inlet go to Harley and get there exhaust clamps. Very heavy steel construction. Has strength to seal the muffler to the pipes. Even with adapters.
Leo