It's a great early Seamaster chronograph with a caliber 321 movement from the late 50s or early 60s as you indicated. It is gold or gold-capped I assume. A photo from the back would help determine that. The serial number on the movement will provide a more accurate estimate of the manufacturing date. Wonderful heirloom. You will get the most information if you have someone open the watch (it should be a screw-in caseback) and post photos of the movement and the inside of the case-back, clearly showing all numbers (serial number and reference number).
As a guess, the reference number may be KO 2907, but that's really just a guess (see below) and there may be other similar references. In any case, the reference number will be clearly indicated inside the caseback.
