Yep I was thinking that frame number looks quite distinctive.
I had a look at the asian guide after I posted since the serial number reminded me of something I'd seen.
Closest in there is

S(3) (Japan): sMyxxxxx [but that would be month code 'Y']
S(4) (Japan): Sy mm xxxx(x) [y = 'Y', month = '87']
SANKI (Japan): Symmxxxx

But the serial number on this frame seems to be "SY87050058" which is at least 1 digit too long.
The only codes that might fit are

SFxxxxxxxx [F = fortnight alpha character = 'Y']
SMxxxxxxxx [M = month character = 'Y' - nope]
SYxxxxxxxx [Y = year alpha character = 'Y']

But I don't see them in that list.