Yes the caprice and Olds front bumper covers work, but the RMW grille pushes them down a little. Look at Brokecellos ride, he's got an OCC bumper on his.
ALso you could look up flash gumby's ride. He took a Marauder front bumper, cut it and welded it to the top half of of RMW bumper for a very stock looking aggresive bumper.