Very interesting. I've never seen an MBW 1680 with the lugs engraved with the appropriate ref. It's always been 5513 that I've seen. However, everything else looks correct, even down to the actual engraving between the lugs (I could be wrong, but I believe the copies of the MBW had the lug refs and s/n lasered instead).
Perhaps there is a new generation or run of MBW's. I do recall seeing some variations coming with the correct sized lug holes drilled. Perhaps they changed the ref between the lugs as well?
The lugs, CG's, crown, lug hole placement, caseback shape, crystal, dial, movement ring, bezel construction, bezel and insert all look correct very MBW characterisitc. I don't recall if the back of my case has those machined grooves or not.