'First Series' - these would be from approx Sept 42 and earlier. The Closed cabs in particular, and anything before that. These would generally be closed cab with all steel beds. 25A 6v Positive ground, Series I hydrovac, normal oil pan. Rubber steering wheel. Die cast carb no fuel level plug
'Second Series' - These would be from approx Sept 42 till Late 43 (Oct-Nov). These would be the 'first series' open cabs, trucks with wooden beds and slick running boards (no pioneer tool mounts). The change to 40A 6v Neg ground, Series II hydrovac, deep sump oil pan. Wood steering wheel. Die cast carb w/fuel level plug
'Third Series' - These would be from late 43 till end of production. These would be the open cabs with composite or bolted steel beds, and with tool mounts on the running boards. Series III hydrovac, composite bed, Late style regulator and cast iron carb.
The original 'six series' are split by, at times, some very minor points in terms of construction. While the three groupings will embrace much more in terms of production changes, I doubt that no 'series groupings' will cover all changes satisfactorily.
