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.
P code left.
P code in rear. Can easily see the undercut on the later hammer in front, also the evenness, as the older style is tapered.
Here's the 68 AD code hammer, with appropriate spur, in my 57 P code gun.