If this is a 720 (and it might be), it is a repaint with a non-original fork. The vintage trek catalogs are online and you can look at them. Over the years that the bike was manufactured, it came in a few different colors but red was not one of them and it did not come with a chrome fork. Also you will want to look at the Trek 600 series as some of those also came with cantilevers.

Why do you think it is a 1983 Trek 720? Here is the url for the website with the catalogs: http://www.vintage-trek.com/TrekBrochures.htm

If you look at the 1983 Trek 720, you'll notice that not only is the color different but so is the seat stay cluster. Looks like that seat stay cluster was used in a little later bikes; here are the '85 touring bikes, http://www.vintage-trek.com/images/t...rekTouring.pdf