9 7 3 , ▁the ▁C ut lass ▁Supreme , ▁like ▁other ▁G M ▁mid - size ▁cars , ▁was ▁red es igned . ▁Hard top ▁models ▁were ▁replaced ▁by ▁new ▁" Col onna de " ▁sty ling ▁with ▁fixed ▁center ▁pill ars . ▁Conc ern s ▁over ▁proposed ▁rol lo ver ▁standards ▁caused ▁many ▁autom akers ▁to ▁phase ▁out ▁their ▁pill ar less ▁hard top s ▁and ▁convert ibles ▁throughout ▁the ▁ 1 9 7 0 s , ▁and ▁the ▁C ut lass ▁was ▁no ▁exception . ▁Despite ▁some ▁initial ▁controvers y ▁over ▁the ▁disapp earance ▁of ▁hard top ▁models , ▁the ▁new ▁ 1 9 7 3 ▁G M ▁mid - s ized ▁line ▁proved ▁highly ▁successful . ▁C ut lass ▁Supreme ▁coup es ▁had ▁a ▁unique ▁roof line ▁with ▁vertical ▁opera ▁windows ▁not ▁shared ▁with ▁other ▁C ut lass ▁coup es , ▁as ▁well ▁as ▁unique ▁front ▁end ▁sty ling . ▁ ▁The ▁C ut lass ▁line ▁soon ▁became ▁Old sm obile ' s ▁biggest ▁s eller , ▁account ing ▁for ▁ 4 3 % ▁of ▁the ▁division ' s ▁total ▁volume ▁in ▁ 1 9 7 4 , ▁with ▁the ▁C ut lass ▁Supreme ▁cou pe ▁being ▁the ▁single ▁most ▁popular ▁model . ▁With ▁rect angular ▁head light s ▁newly ▁legal ized ▁in ▁ 1 9 7 5 , ▁the ▁C ut lass ▁received ▁a ▁fac el ift ▁for ▁the ▁ 1 9 7 6 ▁model ▁year ▁featuring ▁quad ▁head light s ▁and ▁a ▁water fall ▁gr ille .