Not sure how you are going to do the classes though a good way to do it is to have your basic units (Rifleman, Grenadier, machinegunner, etc) because atleast the British anyway Regimental flashes and sometimes even rank slides were taken off so an enemy could not find out what you were and if he knew your plans, where you were going so it would be rather accurate instead of going the NW method of have regimental classes. Not sure if this would the same for other countries especially Germany with their very pimped up uniforms.
Also British commonwealth would probably be a better plan then you can have British, Canadian and possibly ANZAC (Italy campaign?). bearing in mind the uniforms were different between Canadian, British and ANZAC.