Hi Martijn,
Mine measured about 17.75 between the lugs- looks like this was trimmed down to fit something else or has different sized endlinks than the Seawolf would have taken. You have all 13 links which is good, but to use on a Seawolf you would probably have to source endlinks. It should have a date code stamped in the clasp as well- may help you narrow down what else was in the Zodiac catalog at the time to see if it was fitted to something else.
I should mention that mine is a Gen II with ‘64 date code, I don’t know if the Gen I had narrower endlinks (these bracelets were used on both) but US sizing was in English and not metric for many watches so the odd sizing speaks to that.