The squared off (non beveled) nameplate was for the standard prism finder.
I had this same issue.
Luckily I had a parts body that had a beveled nameplate and I swapped them.

There was also a mod to the mirror box component that allowed FTN meter finders to fit. There is a ridge on the top of mirror box that prevented the FTN finder from mounting on ealier bodies. This mod happened around '68 I believe and is designated by the "red dot" bodies at first. They later dropped the red dot as all bodies had the new style mirror box.

Go here
if you don't have the time hopefully someone (John) with the exact info will reply.
I don't know if earlier Photomic finders fit the old nameplate and un-modded mirrorbox.