The Comstar wheels are different in that the rotors, especially on the front, are made to fit the calipers that were used on the '78 model, which were placed at the back-side of the forks, and the offset of the rotor to the flange were quite different too. That means that you will most likely have to use the forks from the '78 as well. The rotors from the '76F have 6 bolts, the comstars have 5, and are not interchangeable. Probably similar problems exist with the rear wheel. If you wanted to switch to the Comstars, you'll need the forks and swingarm and all 3 calipers from the '78, or you have a ton of fabrication work staring you in the face.
Steve F