Is it 33mm diam.?
If so, it's likely a 7499 from about 1970. Very flat and uses the Cal. 1003 movement. This one came in a number of different, but interesting dials.
There was also another thinner ref. which used the 1001, the 6115. Both of these did not have the Maltese cross on the dial nor the "&"
You mave to have someone open it to see if the reference is on the inside of the case. You can also get the csae ans S/N numbers of course, although the case numbr may be on the back.
I think it may be 33mm -- I know it is a small case. I do not have access to the watch to open it up, so it will be hard to confirm. But your educated guesses are probably correct. Thanks for taking the time to reply, dear Joseph.