First model Schofield extraction issue

[Old Dave]

I put this in "antiques" perhaps a mistake. Hammer, trigger, hand, cylinder stop & cylinder all operate as they should. Amazingly, the bore & chambers are all free of pits. 6 rounds with primers only go "bang". Extraction? Bad news. I experience MAYBE one-half inch of lift with brass failing to clear & course no "snap back" or return. My book "Smith & Wesson Sixguns of the Old West" has excellent parts diagrams & disassembly tutorials. I remove the cylinder & stud holding the extractor star, pulling the assembly out the front to find that the spring is in pieces. Not an impossible fix but good reason for no return. Off with barrel assembly where I now see the extractor cam & associated bushing. Now I find drama. With my cam orientated with the cam in the book, I find the notch is in a different place & the cam in the book, has a "flat" on the bottom which mine does not. No wonder that my "lift" is nearly non-existent. My notch would engage the extractor pawl considerably later. Engineering change? Wrong part in my gun or ??? My serial is 739