A couple of things I learned thru this ordeal.

The rear brackets I had were indeed 70-72 style. I bought a repop bumper and installed it just fine. I did buy the 70-71 rear bumper filler but found out it was $50 wasted since it wasn't needed. The 72-74 tailpanel must be designed different???

As for the front. I did happen to have 71 front brackets. After pulling my 73 brackets to prepare them for drilling I decided to check the 71's. They match up to the outboard holes and the bumperette hole but obviously not the top hole. I installed the 71 brackets with the 73 bumper and just plugged the top holes with a spare pair of bolts. Downside is the inboard holes in the 73 bumper are round and don't have a square for the carriage bolt to engage. It tightened up by friction.