That's right Beaumont, fully agree on the L and HRO CER alignment.
Other Mark IV vs. Mark III differences I see:
1. The coronet is different altogether
2. The Swiss - T < 25 is closer to the tick marks
And last but not least:
3. The VERY open 6's
That is not to refute that it could be a replacement but IMHO it is not the same as a Mark III.
To add more fuel to the fire, I've combed Chrono24 and e-bay and found a handful of examples of this dial (amonst many white 1680's) and they all seem to be in the 1978 serial range. Strange coincidence if its a service dial...
Thanks for the tip Marcello.
I'll see about taking the dial off in the next few days (to add some suspense). If its a service dial, I'm buying drinks next time you're in Paris otherwise its a nice bottle of Valpolicella in Italy
Kayvan