Replace the receiver. The receiver is opened up to allow for he two extra parts by there dear thus the need for the block/shim. Without it the sear and disconnector would have room to move from side to side.
Dang. That's what I figured. Oh well, I'll just do what I can with this one and make sure I get a Series 70 frame when I build one.
Alas, the demons in Kalifornia got the idea that guns kill folks if dropped on the floor, so they demanded that gun makers come up with ways to prevent guns from shooting and killing folks when dropped. The firing pin safety block was one of those ways.