The reason I put 1960 out there as a suggested year is this style tank first shows up in the 1960 catalog. This is despite this style chain guard last seen in the catalogs of 1957. While it is possible old chain guards could still be around a couple of years after they are officially obsoleted, it's less likely that a tank is used that is not designed yet.
It is also possible for the tank to have been added later but I find that very unlikely. The common practice for most boys of the era was to strip down a bike, not add tanks to it.
I would not be surprised if the serial number showed a 1959 manufacture date but it is just a guess at this point.
This mis-mash of parts is very common with Columbia's.
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