Chronomat PM'd me with some details- And after taking a step back and giving all the elements of the equation some thought, it makes sense.
The watch has a 6.7M serial, putting production around '80/'81. This is period correct for the crystal style, the tube etc. OOPS! Have to edit here... I just went aand re-read chronomat's PM; his serial and case verification was on his 16550, and NOT his 5513. Sorry for the mis-understanding... A fault of my own as I only briefly scanned over his PM (sorry about that).