Identifying PCB components with metal tops, no other markings visible
My best guess is these are heat spreaders with no actual electrical connections, intended to couple heat into a rear mounted heatsink for forward side components

The bottom left one is the main tip off

So I suspect these may be nickel plated copper blocks

If they do have electrical connections, try cleaning with isoproyl alcohol and a toothbrush, if you can see a white ceramic with gold connections on the side you may be in military grade electronics land.