That fader switch location is different...my '68 RR has it in the switch panel.
That looks like it's on the bottom of the dash.
Maybe that was a dealership or subsequent add-on?
68 and 69 are different and Rally vs. Standard gauges are different. I have samples of each that I pulled off of cars back in the 70's.
68 Belvedere in switch panel
69 Belvedere under dash
The one in the picture is for a Rally year unknown. Radio Bezel is 2889036 and Switch Bezel is 2864223-2 (not in the 69 parts book)
I have never seen one in a car, this is the only one I have ever seen.