The rear brake appears to be the single spring version of the Weinmann 999 which, if OEM, would place it 1957-1962. This does not seem unreasonable given the seat tube collar. The SunTour derailleur is an obvious replacement, as is the stem, which appear to have an Allen head. I've never seen a screened (?) Columbus emblem like that. Given the apparent era, in conjunction with stamped dropouts and the OP's weight assessment, I probably wouldn't put to much credibility in it. It's not too often you see a bicycle that has obviously had reflectors added to it!