One thing to note is the metal body Nagaokas (MP-400 & 500) are slightly smaller footprint than the other MPs as the ‘corners’ are lopped-off.
Ah, it's narrower! Never noticed that before. Used an MP11 Boron years ago and yeah, they are big cartridges.
Another issue I had with that cart was that the stylus fell off. Twice! You could blame clumsy handling but I've never had the stylus come off any other cartridge. I reckoned at the time that maybe it was difficult to bond the stylus to the boron cantilever but the OC9 has a boron cantilever and didn't have an issue with those.