DO NOT FILE THE FIRING PIN. The problem is the weight of the firing pin. Look at an M1 Garand pin, and see what needs to be done. Just some thinning with a dremmel tool, keeping all work going from front to back. No more slam firing.
I invented the conversion for Century, and still own the original gun. Over 2000 rounds with no problems at all. Clean about every 500. An accurate,1/2 inch preformer. I repeat DO NOT FILE THE FIRING PIN FLAT.