Rear tail panel extension fasteners question

[bull]

Or eyebrows, whatever you call them (example pic below). I tried installing mine recently and the speed nut bottoms out below the threads. Maybe the nuts are wrong. Is there some sort of spacer that goes below the nuts or are they different than the typical speed nut? If so what do they look like and where do you get them?

[bull]

Is this the right stuff?

[68RT440]

those look identical to the original ones on my 68...