Looking at completed auctions on Gunbroker:
12 ga grade 1 Superposed from 1971 with Modified chokes sold for $815.
12 ga grade 1 Superposed from 1970 with 30" barrels and a hard case which received no bids $1295.
12 ga grade 1 Superposed from 1969 with 28" barrels and choked Full over Modified sold for $1005 from a seller in Atlanta.
12 ga grade 1 Superposed from 1969 with 28" barrels and choked Full over Modified in fair condition sold for $755.
It is challenging to provide an exact value for a 52 year old firearm, but hopefully this info will help provide a general price range.
12 ga grade 1 Superposed from 1971 with Modified chokes sold for $815.
12 ga grade 1 Superposed from 1970 with 30" barrels and a hard case which received no bids $1295.
12 ga grade 1 Superposed from 1969 with 28" barrels and choked Full over Modified sold for $1005 from a seller in Atlanta.
12 ga grade 1 Superposed from 1969 with 28" barrels and choked Full over Modified in fair condition sold for $755.
It is challenging to provide an exact value for a 52 year old firearm, but hopefully this info will help provide a general price range.