..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