Yes, you would have to in order to make up the difference in length(2 or 4 inches). Coldwar sells a kit where the fake can/barrel extention makes up the whole length issue. It covers the whole barrel plus the 4 extra inches. They said once they would possibly sell just that piece but never really inquired further.
http://www.calguns.net/calgunforum/showthread.php?t=61378
http://www.calguns.net/calgunforum/showthread.php?t=61378