Like Danny, I was going to put the ferrules in the tops of the doors. Couldn't do it.
Yes, they'd be a little ugly. But also: the shape of the door is all wrong to make them work.
I set my side screen project aside about 2 years ago...
The way forward is to make a Speedster style door top trim piece. Best to shape it like a long wedge, like the original Spyders had—but make it about twice as thick. About 7/8 inch should do it.
A 3/4-inch slice of hardwood, carved to conform with the door shape (this will take many hours), then fixed with three or four 1/4-20 studs for mounting, drilled for the ferrules and covered with vinyl that matches the car's interior.
Either that or make a mold off the door tops and then make the part out of Fibral or something like that. Probably quicker than using ash or oak.