Hi K. You have a 60's or early 70's watch and a nice heirloom. The dial & movement come out the front after the bezel and crystal are removed - that's what a 1260 wrench is designated for. The first of these cases appeared in 1958, marked "USE 1200 WRENCH", then the ones marked "USE 1260 WRENCH" came a few years later. It would etiher have a caliber 34x (x = odd number like 1, 3, or 5 for date) or a caliber 50x inside. Both are nice movements. The 50x was based on a Record caliber 195x - Longines acquired Record in 1961 and rebadged their movements with their own codes. The 34x is an in-house Longines movement. While in-house usually means a more valuable watch monetarily, the sentimental value of this outweighs that.
A wrench is a tool used to loosen or open. In this particular case, it's used to open the watch from the front.