Resurrecting this thread with a question I can't seem to find an answer to - why plane the angle onto the body? Why not cut it into the bottom of the neck heel? Especially if you're building a guitar with a slab body rather than a carve top it may not be desirable to have a gradient at the neck end of the body, and it strikes me as potentially being a little bit simpler? Use the trick as described by Ben to work out your angle, draw it onto your neck heel, make a single. accurate cut with a Jigsaw/Bandsaw, do some sanding to get it smooth, and job's a good 'un? Plus you retain a flat body (I'm looking at my PRS Starla and that definitely doesn't have a slope planed into the front of the body. Yes they probably did it on a CNC but still, it's an aspect of the design one might wish to replicate if building a guitar at home...?
