" .. which ones work better .."

I have Percy's on the Duster. They work great. As far as cutting flanges.
Isn't 3-5 on the same flange and 4-6 also. Don't get the 1-3& 5-7. 2-4&6-8.
I can see cutting the whole flange asm between the outer ports and the
center ones so to cut down the chance of leaks if it's warped.