Cannondale started selling cycling gear in 19731) and didn't start selling touring bicycles until 1983. Cannondale uniquely used oversized aluminum tubing in their American made frames which quickly became an industry standard. In 1988 Cannondale was sold to Dorel Industries, which also owns Schwinn, GT, Mongoose, Charge and Caloi. Cannondale remains a successful bicycle brand today: link.
Cannondale was founded in Wilton, CT, next to this train station.
The SM-500 had a Aluminum frame, 24” rear, 26“ front, bmx seatpost and rear brakes with a sprung Brooks saddle and Shimano XT derailleurs.
1984 SM-500 vintagecannondale
The SM600 was an upgrade from the 1984 SM-500, with full SunTour components, including decent brakes, seatpost, better Nitto handlebars, etc. The SM500 remained with the same components, but with down-graded skinnier, smooth tires.
1985 SM600, vintagecannondale
Now with 26” wheels, but spec'd with 26 x 1 1/8“ tires 3), which are narrower than most touring tires. Swap the tires, and it was the bike to get.
1986 SM600 reddit