You can probably repair the metal threaded insert pretty easily. If you reuse the same mounting hole, I'd fill the recesses where the insert's tangs were installed with a thick repair epoxy paste like PC-7. If you're concerned about any possibility the epoxy will get in the insert, you can make sure the threads stay clean & clear. Take a short length of 1/4" x 20 threaded rod, coat the threads with vaseline and leave that in the insert while the repair cures. Good Luck! Those Danley's look like a beast of speaker to move around!