73 swinger rear bumper fit 72 scamp?

Actually, yes, this swap of a '73 Dart-except-Sport bumper onto a '72 Scamp will work. The different bumper setup Burntorange70 has in mind started in '74, not '73. The Swinger bumper will have different taillights than the Scamp bumper, and there's a reinforcement plate behind the bumper bar in '73 that's not there in '72, but they are bolt-for-bolt interchangeable.