I've got no time for loud pipes. Steve of Hillside Cycles had told us often that a Supertrapp 2-into-1 gives great results. I have one and it is indeed great, gives excellent torque and smoothness, while not being too loud.

 

It would be advisable to get all the info on the mods to the heads and start a log. valve size, intake and exhaust port sizes, combustion chamber size in cc's, flow rates and springs. This way if you ever want to make any changes at all you'll be able to do it right.... If they do open up the ports you might want to send them your intake to have it port matched... exhaust is pretty important but when I did the run with the older python lll's I didn't lose much at all and they were only 1 5/8 pipes. Attached is the dyno run with a correction factor of .99