front of model, rounded and straight. the rounded front has a little lip that extends out from the bottom. the straight front is even across the front.
plus a slight difference on the base plate. the line that runs from tire to tire below the rivet is high and low.

http://img296.imageshack.us/img296/2084/fordgroup645noseig2.jpg
http://img296.imageshack.us/img296/2825/fordgroup645nose1bk0.jpg
http://img181.imageshack.us/img181/8915/fordgroup645nose3vt4.jpg