I ask about either of the Czech proof facilities as in 1974 your sporting weapons passed thru either the Brno or Prague & I'm leaning toward Brno. But either way, you should be able to take the images of the datastring on the water table & on the extractor bar and the will have it listed in their ledger. If it isn't in the Prague ledgers, then it will be found in the Brno.

Cheers,

Raimey
rse