This is '78-80, just minor differences in the headlights/turnsignals, '80 has 4 small rectangle headlights
'81-87 is this, minor differences between years on grill/headlight trim...and of course the '83-up Monte Carlo SS and AeroCoupe are on this body style.
73-77 this is the body style, '73-75 have large round headlight, all years have different drill bar patterns, '73 has slight different tail lights and rear bumper as it didn't have the 5mph energy absorbing crap yet. '76-77 only difference is '76 ornament in in grill, '77 it is stand alone "gunsight" on header panel. '76 has just one grill bar on taillight bezel, '77 has 4 bars.