This supports the heater on the trans tunnel, or at least it did on my 73 vert body. Very heavy!
I started scraping out the sound deadening material and it is up to 0.25" in places. That stuff is everywhere. I'll bag it and weigh it when done, but there must be 8 lbs of it.
It cuts down on cowl shake by triangulating the birdcage. It was not there to just hold up a heater core. George