I would not use the aluminum Fat Boy silencer on anything other than a stock engine that is making 50 hp to 55 hp and then I would limit the time of full throttle blast to only a few seconds at a time. 

The piston overheating problem with the over restricted Paul Turner pipe and Fat Boy silencer will not show its ugly head when making 3 second or less long dyno runs even if you are making 10 back to back runs lasting less than 3 seconds each.  It will not usually show a problem running 100 yard long drag races unless the engine has some serious porting and big carb.  If you are running up long sand hills or riding where the throttle is held open for 10 seconds or more you should modify the stinger and silencer to have at least 1.25" ID from the tail cone to the atmosphere. 

It has been my experience that Lt 500s that are surviving when ridden hard that have the small stinger and Fat Boy silencer are not tuned to make good power and or the porting is screwed up.