[Milsurplus] Odd USN ART 13 front panel section, engraved plastic

[Boeing377]

Bought a junker ART 13, no signs of ham conversions or tampering, still had USN freq chart on front with NAS North Island freqs etc. It's missing some tubes and is dirty, but I think i'll end up restoring it. 

What's really odd is that the panel which houses the two meters is 100% plastic, with very neatly engraved markings. I am tempted conclude that this was done in the Navy, perhaps to replace a damaged panel, but no other part of the xmtr shows trauma, no big dents or bends, just the normal scratches. 

Has anyone else seen such a panel?

73
Mark