I don't know the differences between the 1973 and 1974 so I would say whichever modifies easier into the other. I agree with futurabat. Full trim and an opened hood is best for me. I've tried putting trim like side chrome on and it's never straight. Those are the cars that get banished to the back of the room.
Main differences are the grille and tailights..the '73 has quad round tailights, the '74 has dual rounded trapazoidal tailights..'73 is the better looking of the two years, IMO.