Just found an old 15" Crescent wrench like yours in a old rusted tool box, it was missing the adj. thumb screw & retaining pin.
after cleaning up all the tools, I found the Adj screw & very rusted pin in bottom of box mixed with debres.
look like the pin was too rusted, so I used a short bolt with same dia & threads to hold the thumb screw.
cut off the head, cut a slot, works fine.
This model is Drop Forged steel, not alloy.
"1930 Crescent introduced a line of alloy-steel tools under the "Crestoloy" trademark"
does this mean the wrench is pre-1930?