If you are shortening it so the cowl slips on better, you can cut the stack inside the cowl short then use silicone heater hose or the silicone exhaust stack hose Tower sells to re-connect it once the cowl is on.
http://www3.towerhobbies.com/cgi-bin...?&I=LXRVB9&P=0
Lots of choices...
http://www3.towerhobbies.com/cgi-bin...7&C=GMCTRA&P=0