OK. All of the items shown will fit any of the Atlas built lathes except not any of the 6".
On the subject of the 3AT collets, the "AT" may have been specified or chosen by Atlas. However, it doesn't appear that Atlas ever actually made any of them. They had them made for resale, just as they did the chucks and the various collet closers over the years. Atlas also sold 3C if you asked for them. And I've seen indications that at least Logan and South Bend sold 3AT's. Bass Tool & Supply here in Houston still stocks a few of them along with the 3C.