A friend of mine used to run the registry for 1969 GTX's and there are several 69 GTX's known platinum with pewter int.

a local friend of mine has a 1969 GTX hdtp with pewter interior ( buckets with console ) and factory air.
The only known 69 X known in these colors and A/C

I think there is a black A12 roadrunner in florida with pewter interior