There is probably a better answer, but for starters if you're using system 7 it should say on the "About this Macintosh" page (from Apple menu) the model of the Macintosh that you're using. Also - the backs of the Classic and Classic II are different. On the back of a Classic II there should be a microphone port. If you have a Classic II back plastic and there is indeed a microphone port inside the hole, you definitely don't have a Classic logic board inside because Classic doesn't have a mic input. In fact, if all the ports and holes match up I can't imagine that you could have any motherboard but a Classic II.