Having a milling machine would be a huge help. Basically you make slightly under sized templates to match your top and bottom tangs and then mill each side staying a bit short of your target in both depth and width. I would start with something simple to get the idea, a 1895 Winchester or something similar would be a great first project. It could be done with a drill press or router as well with a bit of careful set up. Building from a blank is a great way to learn to most important aspects of stock making. Do you have Westbrook's book?