I assume those templates are for 340/360 size port head. If they are I would not use them on the 318 port size head because it would take so much material to open them up that big you would probably hit a water jacket. I guessing the reason that they don't make 318 size porting templates is because if you wanted a port much bigger than that you would use a 340/360 size port head. What you could possibly do though because the ports are the same basic shape just smaller is calculate how much smaller the 318 ports are from the 340/360 ports then reduce the porting templates the like amount. For example if the 318 ports are 20% smaller then make the templates 20% smaller.
Chuck
