I ran into the same situation with a P code.
I have a P code 336RC, which is a 1957, however there is a R code, listed as 1957-1958. Now getting to spurs, obviously Uncle Mikes has the Pre 83, which covers 82 back to 57. Now comes the hitch!!!, my P code 57 model doesn't seem to fit this category of hammer spurs., So I guess there's an early 57, and a later 57 model year, for certain things, hammers being one. Pic below shows my P code hammer, in the back, compared to a 68 AD model, which obviously uses the Pre 83 spur. I believe there is an old Williams #36, no longer offered, so its an Ebay, Gun Shows, etc. deal. So for the time being I used the 68 AD hammer. I thought I read awhile ago about hammer width differences, but it didn't seem to matter in this instance.
A few pics.

P code over AD code.
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P code left.
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P code in rear. Can easily see the undercut on the later hammer in front, also the evenness, as the older style is tapered.
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Here's the 68 AD code hammer, with appropriate spur, in my 57 P code gun.
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Last edited by Skooter; 01/08/17.