Those metal brackets aren't to hard to make. I had a 75 Olds that had one 6x9 in the back from factory. But the hole and grill were on the other side. So I bought a set of new 6x9s and used the factory clamp on one side. And made my own clamp (redneck style lol) out of 2 coat hangers. In the end, the one I made was a lot more sturdy than the original one.
So if you get one of those sets, just make your own brackets.
So if you get one of those sets, just make your own brackets.