I think all the MTB frames were the same in 1987 but there was a choice of 24" or 26" rear wheel on certain models, which obviously made for a different frame if only in geometry. Best way to equate it with a Cannondale branded model would be to list the components and compare them to the 1987-1988 catalog specs. I can't tell much from your photos except that it's a SunTour equipped bike, so that rules out the models that came with Shimano.