The only marking on the rifle is located on the side just under the bolt handle it reads sheridan products inc racine wis.- made in usa i have taken it apart nothing else. The rear sight is pinched on, no screws to hold it, the safety is located at the breach, has to be held down to fire, just above the safety it says hold down to fire. Does that help?
It has a beautiful walnut stock, and rich blue. Along with the above markings in the title, it has a small # of 5691K, on the left side of the receiver. I oiled it, and fired off some pellets today with just 5 pumps.
That site you gave is only for guns with serial numbers. Colt diamondback serial number list. I was told that sheridan didnt number until in the 60s any further heip is greatly appreciated.