Asides from the skirted front fenders and the different radiator you mention... and basing my comments only on observation:
N1 and N2 have a completely different dashboard, with big round instruments in the center and a couple of glove boxes at each side.
Bumpers are one piece, curved downward in the center in the case of the front one.
Radiator emblem is very similar but different: REO in big letters, and Royale under it, instead of the Reo-Royale and Eight under it, as in 1931-32.
Apparently the grill has fixed vertical bars, verus the thermostatically controlled ones in 1931-32, which makes me think that for 1933-34 they already had an in line thermostat.
And of course, the possibility of the semi automatic transmission.
But again,this is only based on observation. There might be a ton more differences that I couldn't spot.
victor