So I got to do it, I a going to chop the Chevrolet and do 1940 Mercury style side gl***. I have some questions, I see some true hard topped style and some look like the gl*** rolls up in a custom chromed channel, do the hardtopped cars just modify the door top to make a straight run at the wing window area? And some use the front door frame surround without a wing window and roll up gl*** in it, I like this style, and the HDTP style. I started to peel doors apart tonight.
I would say it depends on the degree of difficulty you want to take on and how proper you want the finished job to be. I would suggest that some of those pillarless versions may be done that way to avoid the task of making genuine sealable windows that go up and down.
Check out the custom car chronicle forum. I believe that a lot of these are originally frames that do not go down. Looks like the front door is already pillar-less, so you are halfway there. To make these I see guys forming C Channel for the main shape. IT seems to be a lot of work. Maybe check out some of the sledgecustoms posts He seems to do a ton of these. also some good post on the bending of the frames https://www.customcarchronicle.com/forums/topic/39-cadillac-sixty-special/page/17/#post-19659
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