I mix these up also. there's just to many used machines out there . here I said like a model 15, the under pinning is from a 15 but the head ) take up system is that of a 66.
These were early to mid 70's machines, made when singers was pushing the touch n sews. meaning these were the cheap basic machines, which turned out to be almost bulletproof
oh there is one major part that is plastic and gets broken, because users get sloppy . the hook/shutttle retainer. it hinges like a door so often when it's open it gets banged and cracks at the hinge, you can buy new parts..
seems like there just under $10