The old guns didn't have the hammer block safety like the new ones. The hand you have pictured is operated by a spring inside the trigger so you're going to have to take it apart to install it. You may have better results if you give the strain screw some turns and tighten up the mainspring. Unless I missed it this gun isn't registered is it? If you get the long barrel on it they may register it for you. As was suggested, armoured car companies carried a great many different pattern and caliber handguns right up until the AG's office put out paper on what was to be allowed. That was about 1998. Up until then guns could be brought into the company and bought for a dollar so the employee could use his own gun. I know lots of guys that did it.