Each boom vang is custom made. The measurements we would need are as follows:
The distance from the underside of boom straight down to the lowest point of the mast where the mast bracket can be mounted
Templates of the aft part of mast and the underside of boom. A simple way of doing this is to take a piece of soldering wire and bend it around the aft part of mast, then trace the shape onto a piece of paper. Repeat the process on the underside of boom
Size and make of boat