Where to mount some head johnny 94's (there just about unmarked)

So I just got some head johnny 94's and some mojo's from the rep I know. The only mounting line on them is pretty far back and says 3.5 next to it. Don't know if thats 3.5 from core center or what. Anyone know how to find core center, obviously true center would be easy but there's a lot of shovel in the tips (there from the big mountain line, i just wanted a ski fatter than what they offered in their park line) so I kinda want to know where core is. I asked him and he didn't know.