Yes, diversity of numbers is something to get used to.
Units in Vietnam generally operated at 20% below official strength, often at 30%, or on occasion more, so essentially an average of 2 or 3 figures would be absent from any individual squad. Obviously it wasn't spread out so evenly though, but effectively each platoon was essentially short of between 9 and 12 men at any one time - effectively one of its four squads.
The 'weapons squad' was often used as a pool to replace 'missing men' (sickness, leave, casualties) and to provide each of the three rifle squads with an M60 (with one added from the battalion MG platoon). The recoilless rifles were rarely carried, so this also provided spare riflemen too.
Squads of 5 men or less were considered 'combat ineffective' and 11 (including the Staff Sergeant leading the squad) was the maximum number of men it was felt could be led with any efficiency (the Marines obviously felt differently) by a single squad leader and even then, needed to be broken down into two 'fire teams' (ideally evenly), each led by a sergeant.
In essence then, your Army squad will have a 'Staff Sergeant' leading it and up to two Sergeants (or men acting as such) as fire-team leaders. Two men will have an M79 each and one will almost certainly have an M60. The rest of the men have M16 rifles and I suggest rolling 1D4 to determine how many of them there are.