Finish (nickel or blue) may also affect value.
The M27-2 was produced for a long time, 1961 - 1982. Earlier ones (serial number would start with "S") are more desirable to some of us. If you post the serial number (xx the last two digits if you like), someone could tell you the approximate shipping date.
If the target stocks have a diamond in the center, that would also be a plus.