Howdy Marc, for those who haven't spoken with him, he and I went over some of this on the phone over the holiday weekend, he's generous with his time
OK first off, cool wheel color combo for the Vette, now if you can fix the car so that it's a Viper you would be all set!!

I had said:
"disassembled them the second time to sand the contact points and verify they were safe"
I cleaned up/sanded off the ample layer of rust from the calipers where the pad's "tabs/hooks" sit. The thinking was the noise was mechanical, not brake squeal, so why on all 4 wheels did I hear this God awful noise at any speed when I punched the brakes? It could of been that the pads were loudly complaining as they moved (they do slide a little from the piston movement) over that rusted caliper area. One other point if you do sand these spots on the calipers put some lube on after. We had this product that was made for doing this, just a tiny amount as well.

The "and verify they were safe" is because we were leaving for a GTG and didn't want to find an oh $hit while on the road. After the second time the noise was still there, but after our trip to Fleetwood in Canada it's gone, so I feel it's become a non-issue at this point only because I think my "miss-matched directional front/rear" rotors may of played a part initially. The miles from the trip seemed to of stopped the noise, but the rotors still need to be swapped out to make front and rear match.

I was suspicious that the dust, which is black black black and now dissipating, was from the wheel well area. I had sprayed and cleaned the wells up, also used compressed air to blow everything, but that stuff is so fine it hides everywhere. I have to say I've taken the wheels off 3 times and washed them completely, the black dust was still pretty heavy. The rotors had it packed in the slots and holes too.
This is on a car that always had the wheel wells washed out/up so if someone hasn't been cleaning the dust off I can imagine they would see black dust for a while.

Attached are pictures showing the dust on I believe a passenger rear and front. Also a shot of the spots where I sanded the rust off the calipers. The pads and rotors have not made any of the squeal noise some people claim ceramic pads will have and they stop the car great! Some butt head came inches close to side swiping us in Canada my car stopped neck snappingly fast!
Also credit to my loving husband who is the person who jacks the car up and physically gets the wheels off. My hands are not strong enough to do that stuff. Also I have him check my work so if I screwed up he'll catch it. Thank you sweetie.
(FYI Marc the set screws fit on all 4 rotors for our sets)