Those stocks are from a much later time period probably post-WWII. Yup, 1927 is the date because of the large ejector rod knob, but there are 1928 and 1929 guns with serial numbers higher than yours that shipped both earlier and later. Inventories must have been high in those years and the factory did not ship in serial number order. Great heirloom.
As for value, the incorrect stocks negatively affect value, but gun looks to have original finish. Problem is that there were already a half-million 38 M&Ps made by the time your revolver left the factory, so values are low. Also, blued guns often are valued higher than nickel, so a guess at value would be around $350 - $400. Of course, it is priceless as an heirloom. Get that letter.
The stocks that are correct for your revolver would look like the example below.