On panel 6 there is an arch, sure, but the panel as a whole is more of an “Antients” coat of arms. Are there other reasons to assume “Royal Arch” on panel 6? Interestingly, an image such as this can still be found in Royal Arch books.
This particular image is from General Ahiman Rezon by Daniel Sickels (1870). Of course that could just be inspired by the emblem of the Antients rather than the other way around.
The two images in the top corners are Royal Arch symbols according to some. The mitre and the breast plate of the High Priest respectively.
