I just installed an ARB snorkel on my Montero and wrote a post about on my WCXC blog.
Here’s the biggest tip of the whole exercise: use the template only to drill the big, 86mm hole. Mark the small, snorkel bolt holes as well but use the bolts themselves to determine their exact positions. The template may not be accurate — it wasn’t for us. Use the same method for determining the positions of the A-pillar holes and you’ll be dead on.
Here's the post: ARB Safari Snorkel Install