I found several of these boards mounted on 30ish pound heat sinks. Once I remove the boards, I see these thick pieces of what appears to be copper underneath. I took a side view with a quarter for reference.

What grade would these be considered?

No precious metals. Mid-grade.
You may find a yard near you that will buy for the copper.
The white disks in the centers are RF silicon transistors. Look under the brass clip holding them down and they may have gold plate wings. No obvious category for them on boardsort and attached to that much"junk" won't get above mid-grade but you may find a way to get some value elsewhere.