i used the perimeter one so it would heat the carb better. i don't know if that's the difference. i asked several people on the reason for the 2 years ago and never got a good answer. i will watch this thread and hope to find out. maybe if you live in a warmer climate you use the full sheet one. by the way if you do get this milled put this gasket in first and tighten them together after they are mounted to engine. do this before you take it to machine shop and don't take it apart to remount like the shop manual says. good luck and hope i didn't steer yu wrong on which one to use, surely someone will knoe the reason. hr
