Basically only two options: .38 M&P or .32-20 M&P. There may have been some .32 Long M&Ps made in that period, but they are so uncommon it is very unlikely this pair shipped on one of those.Now what revolvers would they have come on?
Definitely K frame stocks. The ledge on either side of the top round is the best way to tell the difference. Look at the attached images. Your set has some wear and has been refinished, but will still present well on an old M&P. The bottom edge of the stocks are quite rounded from use as well
K on left and N on right.
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Gary, isn't it N on left and K on the right?