Thats probably not stucco. It looks more like someone had a tool, and used it to put heavy texture on a ceiling, that maybe needed a bit of work. It is done with sheetrock mud and what some call a stomping tool. I would remove the tiles before redoing the ceiling. Its not a huge job to remove them. I would also remove that awful textured ceiling and redo that at the same time. Since house was built in 1974, you have a 50/50 chance of asbestos in the textured ceiling, since they were changing some of the laws about that time.