I found the old cap on the street by back-tracking, a little mashed. I heated it with the torch and re-shaped it; fabed and brazed a cap and outlet onto the stock muffler outlet , with with 1/2 inch male ppe thread, and added a muffler from a large portable gas generator to act essentially as a resonator. Also fabed a bracket/hanger for the second muffler attached to the frame to keep extra stress off of the exhaust pipe. Haven't ridden much, mut noticably quieter, and seems only to have lost a very little power, but will know better after more miles and tests on some steep hills. If it still has enough torque, I really like the extra quiet.
BAIRDCO: Thanks for the tip. Mine was held with 6mm nut on a bolt-stud. If I had it to do over, I'd take the vice grips and jam those threads just below the tightened nut, so the vibes would not unscrew it!