Different case, different diameter crystal...keep in mind that these are made differently than just a regular (mostly) flat crystal. These require a lot of machining to provide a profile that is quite tall like an acrylic Speedmaster crystal is.
Having seen some aftermarket crystals in various Seamasters over the years, the quality isn't quite there when compared to an OEM crystal. Personally I would not want one on my watch.
Cheers, Al
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