Hi, I have purchased the required hardware (2 fiddle blocks) for a basic boom vang. The length of my boom is 12'. The boom comes off the mast approx 2 1/2 feet above the cabin. 1. What measurements does one use to determine attachement points? 2.What hardware are these blocks attached to the mast and boom with? Is drilling holes for self tapping screws adequate to hold the bails?