Anybody try to fit the Hellwig rear sway bar with a 4" exhaust. If so what mods did it need to fit?

Hellwig bar won't work with a 4" exhaust system. You'll have to use a bar made for after market exhaust systems. Several are available - try this thread for more info:

http://www.dieselplace.com/forum/showthread.php?t=127175&highlight=sway+bar