Chester,,, those OM Single Sixes are desirable to a lot of folks if they are in excellent shape etc. Some "extra" value can be placed it that gun has anything out of the ordinary such as a D or an S in the serial number or marked on the frame.
You asked about the 22 mag cylinder. If the serial number is below 150,000 it did not get a mag cylinder as an option. In fact,, when the mag cylinders were added,,, the bore diameter was opened a little to accomodate the magnum. Since you mentioned your gun was made in 1959,, it's POSSIBLE to have been either type as the serial number of 150,000 was passed in 1959. Check the number,,, and if it's below that,, no mag. If after that it could have one,,, but,,, a call to the Ruger factory,,, asking for "Records" dept,, can get you a month & year of shipping along with a correct model info to let you know if it did have a 22 mag cylinder.
It's all in the details,,,,,,!