If it is a Model 40 (or variation thereof), the original guns with the grip safety also came with a small pin in a hole in the frame and covered by the stocks.
That pin could be used to secure the grip safety in the OFF position, meaning that the gun was simply double action only like the modern series 42/042/640/642/940 etc.
Often the pin has been lost, but it's relatively easy to fabricate a replacement.
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