Way cool, Wyatt! No, I'd never seen them before, at least not that I noticed. (I've seen a lot of cars over the years and might have walked right by a car so equipped.
No photo handy, but I've a pair of similar type items for a Herald bonnet. The first Heralds used a wide front side/flasher lamp. At some point, they changed to a much narrower lamp (same as some E-type Jags and 1970 Spitfires and GT6s )used for a backup lamp...and then they changed back again. At some point yet later on, Triumph apparently stopped supplying bonnets or pieces thereof for the small side/flasher lamp, but they did stamp out a bolt-on plinth to cover the big hole and allow mounting the small lamp.
Apparently they did the same thing, sometimes at the factory, on the early Mk3 Spitfire to allow that car's side/flasher lamp to be fitted for a bonnet originally with the two holes for the "beehive" style front lamps. I've seen a couple photos of those.