The headlights were always in the grille on the S2, and on most of the S2As, but there are some later 2As with lights in the wings like the S3.
The S2 can be distinguished from S2A by a few things, but I can only remember a couple at the moment!......
The vent controls on the 2 are operated by quite large (about 1.75" diameter) bakelight knobs, which were replaced on the 2A with small ones (about 1" diameter).
The steering wheel on the S2 has a distinctive style - three sets of three spokes, with a plain centre piece. On the S2A the centre piece was replaced with a horn button (which on the S2 was a seperate button mounted off the steering column). Sometime later on S2A and S3, the three-spoke design was changed for a plastic moulded type with three solid spokes.
.... Although a lot of the vehicles that you see around this age have been modified in some way or other, so it can be hard to tell....