Gordie had it right...at least for Fords.
I owned a 38 Ford Convertible Sedan a few years back (result of failed attempt to buy a Stanley Steamer at auction, had money left...another story). Made 2406 of them. FDR had one at Warm Springs (still there) fitted with hand controls, so he could drive it. 4 door. The center posts, B pillars, were a loose piece that fitted in before top went up. All the windows were roll-up.
Bob L.