I have no idea what brand of strings or type they came with in those days. Since I like a little definition in the sound instead of just pure mud, I would go with a set of short scale GHS Pressurewounds. A little more definition than flats, but it wouldn't stray that far from the original sound. For a brighter sound D'Addario Pro Steels are nice, but I do not know what effect they may have on those old frets. I used them on my Epi Allan Woody that has the two mini humbuckers like on a hofner Cavern Bass, and it gave that bass a much brighter sound. I am currently using a set of SIT shortscale nickels on the bass, which sound good as well.
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