@missblpsnanna I always thought there was some doubt whether it was the original ring? Grandad is wearing one in his wedding photo, but is it that one? I'll get it dated one day ...
I have a photo of Grandad holding me as a baby and he's wearing a wedding ring which, by your calculations, would be the one that you are now wearing...
Charles Green and Son, 9 carat gold, cast in Birmingham in 1958.