Starting with a 'sawzall" blade, clean the surface and design the basic shape of the blade and the hidden tang. Try not to use any portion of the actual sawing area. This is a rough design to use on the grinding wheel. I used a piece of soapstone to mark the metal.
Plan to use the hole at the rear of the blade to hold a pin to anchor the blade in place. Next, using a model of the handle, determine the location of the second hole to anchor the blade to the handle. Use an awl or nail to mark the hole location on the metal. Sawzall blades are very hard and nearly impossible to drill, so we will punch a hole rather than drilling a hole. Place the metal over a hole in a steel plate or block of wood. Using an 1/8" punch, tap a hole in the metal.
Now take the blade to a grinding wheel and remove excess material to create the basic outline of the blade and tang. Use water to keep the blade cool as you shape the metal.