Everything about that bike says 1962 or 1963 - but can't find a pic of a model that completely matches it.
The magneto setup in particular -maybe its been converted from points to magneto - or export models were built to other than domestic specs ?
The internal pushrods like that and 74 x 81 appeared for 1962, and for 1964 the forks were Norton, not AMC.
If I read the description of mudguards and taillight correctly, your taillight is the new-for-1963 version.
And your seat is also the new-for-1963 version.
Not sure where that muffler fits into it, could be earlier ??
So this suggests a 1963 Model 16.
Hopethishelps.