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My manual is a B25000/up rev Apr 1982. I see the -24, but the part number is changed for this extension it shows the manual 670-2339-24 which is maybe a typo. But in my manual from -12 and up the part number is changed. The board actually has the part # 670-2239-24 printed on it.
I have a listing for that board in the service manual I have it is an option 7 only main board for the B250000 and up 475 scopes. So if you need any specific parts #'s I can supply them.