Thank you everyone so much for your advice, on both threads! Cari, those links are invaluable and I appreciate the time you and everyone have taken to guide me in the right direction.
Incidentally, I have to drive in to "town" (3 hours away) next week. When I first got my Morse, I was afraid to use it in case something was broken, so I dropped it off at this dusty little shop where the 80-year-old repair man said, "Well, that's an old one!" He cleaned and inspected it for me for a small fee. I'm going to bring the Ambassador to him next week, and he said he probably has a presser foot "lying around" for it (and a belt, and some other goodies). Whether he does or not, I'm excited to go in and see all the machines he's got for sale. Now that I can identify some of them and their features, it will be fun to view the treasures!