That is a really neat gun! Based on what I am seeing, I believe that your gun was intended to be a model 57 .41 Magnum and was over stamped. The model 29 .44 Magnum and model 25 in .45 ACP would have both been up to the -2 engineering change by this time, but the model 57 would have been a no dash at that time. It did not go to a -1 until the pinned barrel and recessed chambers were eliminated. That's why there was no room for the -2 after they overstamped it 28.