Your original question was about shaping from a rectangular block. You could get triangular strips of different dimensions from your LHS and use the technique described by Minnflyer. You could also use the GP multi sander to sand out the bevels. Very easy to use and accurate. But if you already have the rectangular block, you could still sand out to the triangle dimensions you need using a sanding bar (just make sure it is longer than your wood), and then bevel it. Just more work and a lot more balsa dust in your lungs.........