More of the serial number may be hidden behind the axle-nut washer, or the braces for the fender and rack.
Check out the thread on serial numbers for bikes manufactured by Murray; a lot of good pictures there.
https://thecabe.com/forum/threads/murray-serial-number-project.7014/
I believe that Murray started stamping the serial numbers in a new location on the left drop-outs in the early-middle 1960's?
Though smaller 24"-wheel bikes may have peculiarities, I thought that the detail of the frame design, attaching the smaller cantilever tubes to the top-rear of the down tube, was an earlier design, (tight joint, weld or braze). And, that later Murray attached them to the right-left sides, for ease of manufacture, (or to conform with others).