'34 coupe and sedan doors have an extra sheet metal fold at the rear of the window opening. The '34 windows will crank back a bit (maybe 3/4 inch?) for ventilation before they lower. The extra flap is to seal the window opening when the window is fully raised. Doors will interchange from year to year, so then one needs to look at other details mentioned before.
'33 dash also has engine turned gauge panel that is removable, while a '34 gauge panel is integral with the dashboard. Firewall has differences for hood latching on '34 and '34 also has a notch to hold the hood when it is open. I'm not sure about the headlamp diameter, but the '33 is more pointed to the rear, '34 is a bit more rounded and the cowl lights have the same touches as well. '33 Frame at front cross member has fewer rivets to hold it in, the '34 was beefed up in that area. Plenty more other detail differences I have not mentioned, Ford styling/engineering was in much transition in that era.