Post a pic of your Cooey's current configuration.
Originally they had a plastic magazine, and the keyhole, potmetal magazines simply don't fit. If you've a rifle already set up to use the keyhole, potmetal magazines(Cooey 64B, Lakefield. Savage) then a newer one will fit. Some folks find they have to do a bit of fitting/filing for newer magazines, but I've not encountered that personally.