Notice there are 2 drastic differences between your bike and the one in the Murray ad you posted... The Murray ad shows a cast 2 piece crank and different sprocket. The chain guard on your bike is shaped like an AMF I had from 73 and I bet frame of the bike in the ad hidden under the guard and brace has the same pointy dropout as the other Murray examples posted before, different than yours.
The rear hub on your bike is a Bendix Red Band hub that would date the wheels as early as 62/63 and only as late as 1968. If the wheels are original, that will help you with date range while looking through Wards catalogs for matching examples, found here:
https://christmas.musetechnical.com/