Triangle stock will work on TE or LE that are not tapered. If your TE is tapered you will need to shape the bevels by hand. The easiest way to do this is to lay out your hingle location first. Strike a center line down both TE and LE, locate your hinge holes and drill or slot as necessary.
Use a protractor to transfer the angle needed onto the end of the LE or TE. I like to leave a 1/16-1/8" width at the hingle line where the two surfaces meet. Once you draw your angles on both ends you can either cut the bevel with a band saw or a razor plane. Clean up the bevel with a sanding block. Temporarily install a couple of hinges and line up your LE and TE so they are centered in relationship to the control surface. It is helpful to mark the center on the end of the control surface. Align the LE and TE and glue them in place. This ensures that your moveable surface is aligned with the fixed surface.