I would insure it for at least $2500.
I have a 1942 "byf" like yours (S/N 2011 "l"suffix)
Mine has the same 3 acceptance proofs on the right frame and it also has "42" on the chamber.
My magazine was also a black fxo E/37, but it has an un-numbered wooden plug with an off-center pin at the 12 o'clock position
(BTW, nice photos !)
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