Sorry, it's a '58 model model that's frame was made in late '57. Like a car model year begins. The '57s were different than Hooch's bike. My serial number is "W2" which is May '56 and you know it's not a '56. The first year for Mark II's was 1957. The Jag heavyweight stopped in 1955 and there were no 1956 models before the "new" middleweight Mark II version was released for 1957.
Believe it or not, Schwinn added 1/2" to the seat post bar for 1957 as the tank was in the way for the shift cable so they moved the pulley. In '58 the pulley was back down below the top bar and the seat post tube was back to normal height. The cable runs through the tank on the '58 models instead of over the top, which is how this bike is set up. The front cable clamp on the top bar is also from a '58, designed to move the shift cable lower so it can run through the tank. On a smaller note, most '57 jags had color coordinated grips and the '58s went to white.
If you plan on putting a tank on this bike make sure it's for a '58 or newer or you'll have to notch it out at the front and bottom for cable clearance. My green one does not have the notches, my black one does.
Mike
Mike