I checked those seat belt washers ad I found no trace of red dye on the washers.
Regarding the red dye I saw a original owner, low milage, never restored, sitting in a storage facility for the last 30+ years, 70 Gt 500 at a friends restoration facility this past weekend. Saw it a few months ago just sitting there but now it was completely disassembled. I looked at the fasteners specifically those that we mentioned were dyed red. They were NOT dyed lightly so as to have a redish pink. They were very dark. Almost to the point of being almost brown. Very evident on the shafts which were protected by the frame. I think the new red dye is reformulated because of that whole red dye issue in the late 70's. They said the old red caused cancer and there was even talk at the time that you wouldn't be able to get red dye.