Keep in mind that when Jerry Kuhnhausen wrote that manual gunsmiths didn't have the wide selection of parts that are available today. You'll note that he recomends trimming the rebound spring instead of using a lighter spring and it's because at that time there was only one spring you could purchase, the factory spring. He also shows how to stone the SA sear on the trigger to reduce the SA trigger pull, something that I don't feel is wise and will create issues with "pushoff" down the road. A much easier and safer way to reduce the SA trigger pull is to simply install a lighter rebound spring. Quite simply some of the procedures in that manual were a result of the time period of when it was written.

As for chamfering the cylinder stop, it's was probably an expediant method at that time and "may" still be viable today. However I would advise that any chamfer applied be microscopic in size and done with the assistance of a minimum of 4 power magnification. If you think that might solve your problem it may be worth a try but I would make every effort to make that chamfer NO wider than 0.003 to 0.005 inches in width. Otherwise you may be looking at trying to replace a cylinder stop that hasn't been made for many many years.

Now, in reference to your 1917. The ideal solution would be to fit a new extractor. However, if won't be at all easy to find a new extractor for a revolver produced nearly 100 years ago. Note, if it's a Classic re-issue it will feature Modern parts and be under warranty, so a trip home is the simplest answer. Second best answer is to install a thicker hand, however that may require the pawls for the chamber positions that now time properly to be fitted to that new hand. In addition it may also require widening the frame window for that thicker hand.

Third best option is to peen the pawls that are falling a bit short on carryup. BTW, peening is basically hammering on the top of the pawl to make it "bulge" a bit wider and will require the use of an anvil or steel topped bench to support the extractor. You'll also need a hardened peening punch with a slightly dome shaped face. You will also have to be very very certain that you are working on the correct pawl.

Finally, IMO many of us are much too critical in terms of timing. Yeah, I know that is what is taught today. However these are Combat Revolvers and really weren't intended to be cocked in Super Slow Motion. I'll also note that the S&W manual for current revolvers advises that in double action the trigger NOT be staged. Quite simply, if the timing is really borderline it's not really a problem if you use the revolver as it was intended to be used, cocking it briskly and pulling the trigger in one complete smooth motion. Doing this will allow the inertia of the cylinder to carry it into full lock even if the timing falls a bit short in Super Slow Motion. I'll also note that almost any S&W 6 shooter that times out perfectly with a right handed trigger pull will fail on timing with a left handed trigger pull when using a super slow motion trigger pull.

BTW, I have a new 625 JM that actually times correctly with a super slow motion left handed trigger pull. However, it locks up so tightly that it's right at the borderline for a Hand/Cylinder stop bind. I have no idea who fitted my 625 but my impression is that he fitted it within 0.0002 to 0.0005 inch, which is extraordinary for something that is hand fitted and likely a fortunate accident for me. I also expect in 2 or 3 years of shooting it may start to fail left handed because parts do wear.

Point is, IMO total perfection isn't absolutely essential but it is a "judgement" call. I have a 67-1 that will fail on one chamber in super slow motion and it doesn't spit lead or concern me because that isn't how I use the gun. I'll also note that like your 1917, pulling the trigger gives the hand just enough of a nudge to drop the stop into the notch. If you make it a habit to shoot your gun briskly, IMO you should just leave it alone and just keep an eye on it.

I'll also note that if my 67 didn't carry up with a moderately slow pull of the trigger or cocking of the hammer I would have a gunsmith correct it. IMO timing issues are something that is best left to a pro who really knows what he is doing. Quite simply, it takes Practice to fit these parts without making mistakes and part of that learning process will likely mean making mistakes that will end up costing more than paying someone to fix it for me.