Gibson spacing is around 50mm. So yours bridge is definitely Fender spacing which can be anywhere from 52-55. Here's a blog post about it from Lollar Pickups:
On bridges you sometimes see measurements from center-string to center string (as you used: 10.5mm). On pickups I generally see it from the center of the E string pole pieces. On "standard" AKA "Gibson" style humbuckers, if they don't tell you the width the way to bet is that they'll be 50mm. On single-coils the way to bet is F-spacing.
On Filtertron-style pickups, you'd actually expect the spacing to be wider than G-style. I couldn't find the spacing for actual Gretch Filtertrons. It may not actually matter since their "space control" bridges allow you to adjust the string spacing. TV-Jones makes the most famous clones, and their spacing for the bridge pickup is a little wider than Gibson (51.6), but not as wide as Fender. Fender's Cabronitas (52.5).
I suspect, you may actually have a G-style mini humbucker in a filtertron style case. Most mini-HBs have 50mm spaciing. That's not necessarily a bad thing since mini's are a great sounding pickup that's really similar to a Filtertron. Here's a kinda-sorta AB of the two.
To my ears the Filtertron and the mini-HB sound pretty close. Darrell hears more nuance than I do, but I don't think there is any difference that some minor EQ couldn't take care of--and both sound really good.
I suspect that many mass producers use just the most common bobbin sizes. I haven't cracked open an Asian Filtertron, but I have cracked open a number cheap pickups (like Firebird pickups) only to find more mass produced guts rather than historically accurate magnets and bobbins. I am not knocking this approach. My lipstick tube pickups have Gibson Firebird guts rather than the OEM Dano guts--and they sound great ;-) I did take a look at the Artec Catalog, and their "neo traditional" HB pickups that look like Filtertrons have 50mm string spacing. They are similar in size to the mini-HB's on the next page, and I'd be willing to bet the bobbins are the same if we cracked them both open. Artec's a pretty good Korean pickup maker--and makes a huge number of OEM pickups. I suspect that other mass produced "filtertron" clones do the same.
All just speculation, but you got my curiosity going ;-)
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