Based on my little research it appear that this model 7928/0 was produced in a small time period after the 7928 and possibly before any ETA movements started to appear.
The Calibre 390 was fitted in this model but some confusion is still out there. I hope some experts can shed some light.
From what I have found and many out there seem to sub substantiate the case is that all those 7928/0 were produced +/- 1967 according the to serial numbers for Tudor all starting with 59XXXX which I can confirm mine is 597xxx.
Here are some pictures for some drama. I will add some more later.