: If the bezel is a later replacement, would that make finding a
: replacement insert easier?

Actually the opposite. Finding a replacement insert for the later type is very hard - almost impossible.
We have identified several inserts that will fit the earlier 'non-tramline' bezels, as the Monnin case design wasn't exclusive to Heuer.
If you do a search on here for Monnin bezels, you should find a handy thread with a few suggestions.

Stewart
- Heuerville