Again, his MOS is listed on his separation papers. This is the only way I know of to determine his duties (that is, the only way to do so free of charge). Check with the county clerk of the jurisdiction where he entered service. Some jurisdictions paid a war service bonus and applicants were required to provide separation papers to establish eligibility. Clerks usually required (or made) copies to keep on file. Over the years, veterans have been required to provide separation documents to establish eligibility for an increasing number of state and local veterans programs so you might check with authorities of jurisdictions where he lived from the mid- to late 1960's.
The Army Air Forces was, of necessity, top-heavy with technical and specialized personnel. Most technical schools and specialized courses of training assured an individual the rank of Staff Sergeant upon successful completion. This had more to do with the pay feature than any command authority.