Originally Posted by Sevens

The serial number dates it to 1977 or 1978. You can use modern 5906 magazines or the Mec-Gar equivalent in the 59, or stick to the original 14-round 1st Gen magazines.

I find that the 1st/2nd Gen 59 series pistol is vastly improved with the Uncle Mike’s/Butler Creek rubber grip panels. These are now out of production but can often be found on Ebay and Gunbroker.