Welcome aboard Waggy. GM didn't put specific build dates on vehicles back then. Probably the closest you'll be able to get to a build date would be the build/casting dates from the engine and transmission, if the originals are intact. It seem kind of odd to me that the insurance company needs the build date, usually the year listed for the VIN is sufficient. Your VIN is a '59, breaks down as '59 3100, the digit after 59 is probably actually an "O" instead of 0, which indicates that it was built in Oakland,CA. The VIN indicates 6 cylinder, the casting date is by the starter.
On the Apache name issue, that designation was used from '58-'62, with '58-'59 being the Task Force body (solid axle), and the '60-'61 being the Jet Inspired (independant totsion bar suspension).
