Question about my zion 660 69er rigid ss?

So im rockin a zion as a 69er full rigid, but i want to throw a suspension fork on the front. I know that I could do it if i went to a 26" wheel in the front, but i like it as a 69er. I've heard that the geometry of the bike would be messed up if i kept it 69er with a suspension fork. Does anyone know if this is true? The bike rides awsome but i want some koosh!