First verify your Bronco had rear seats originally. My 66 didn't; but had dimples in the metal floor. I replaced my tank so while it was out, I welded in the nuts that the factory didn't provide. In your case, I'd suggest pulling up the covering (?). OR you may get close by measuring another stock EB then cutting through the covering. The stock rear seat base will cover up a small amount if your initial hole is a little off. Once you find one, the other three will be easy.<br>Good luck