Thanks Rob. The serial is 61XXX so I'm guessing that's relatively early on if the 3647's started around 54XXX. I wonder if the bridge was a service replacement at some point? The MN marking seems quite common for Heuers, but have you seen the SOX marking before?

: ..is that the movement is a donor / franken. I have also never seen
: a bridge like that and it is rather crudely engraved compared to
: the typical Heuer bridges (not that they were highly decorated,
: but the lettering was much cleaner). Unsigned crown is fine on
: the earlier Carreras (not sure of the serial on this but my
: hunch is that it would fit with unsigned crowns).

: Could be wrong about the movement, but I have looked at hundreds of
: these over the years and can't place another one like this.

: Cheers,
: Rob