Browsing through the posts recently I chanced upon a "topic within a topic". This was to do with the origin of the 3 small square rear lights on the works F1 Endurance bikes. They were ID'd as Ferrari door marker lights. Available as NOS at something like $300 a pair...& we need 3!
I'm in the process of putting parts together for just such an F1 replica & have sourced what I think are a pretty good match for the originals at a fraction of the cost. I had to buy a few sets to get a reasonable price so if you think they are OK reply. Sets of 3, all bagged NOS 12v single filament bulbs. Rubber molding with a removable lens. No chrome surround. In the UK but will post anywhere. £60.00 UK for a set of 3; insured p&p extra

would they handle a 21w stop light globe?

No. The bulb in there is a 5w push fit as you would find in an instrument or pilot light in a headlamp. I haven't see the originals but I suspect as they were door-edge-marker lights they too would be a very small , low wattage bulb. I intend to use high output single LEDs in mine. Easy to get the light output of a 25w bulb from a 3w LED...& much less heat to dissipate.

Fresh pics of the tail light I took at the Ducati museum. Note the pop rivets and the carefree application of the reflective tape.