The guys are correct, a 1680 dial (~27mm) is too large for an MBK/MBW case (26mm). It has to be trimmed down to fit so you run the risk of chipping the finish I've read that one of the members (can't remember who) used a lathe to enlarge the groove for the dial, but that's a whole other level of work.
Another more costly option is to get a Vietnamese made aftermarket case that is made to fit a gen dial.
I was in the same situation with a gen dial and decided I didn't want to cut it down and scrapped that project.
Good luck!