With the Amazon, Volvo use a ribbed and shaped spreader plate between the bracket and the bumper blade. These or a version of them may work with the PV. You say you are going to try a spacer so you're on the right track. Round off the square ends of the brackets where they meet the bumper. The sharp corners tend to dig into the blade and wear a hole in the back due to fretting. It also causes a rust hot spot which will soon be visible from the front. Well done, it's been a long haul of a restore.