1. Plus the door mods aren't easily reversable.
If it's a big-window car they are indeed easily reversible. You need only cut one side of the tab inside the window opening and push it down. You don't even have to re-weld it to go back to vent windows; just push it back up. You could even tack them back in place without damaging the exterior paint. But that's beside the point.
2. Can you get the rubber for the fronts? Is it just a matter of not fitting certain bits of trim?
On the big-window cars I think you may be able to use inner window scrapers on the outside. I haven't had a big-window car in 15 years, though (and it had one-piece windows anyway) so I don't know.
I DO know, however, that you can make your own. It's for a small-window car so it's not exactly your application but the principles should be similar. Volkswagen punched matching holes in both sides of the window opening. So I drilled the rivets out of the outer scrapers and ditched the trim and tin backer. After some measurements I cut rectangular holes in the naked scraper so its lip rested on the edge of the opening. Then I just used the wire clip from an old inner scraper to hold the outer scraper in place. It works great.
I know that the big-window cars don't use those wire clips on the inner scrapers so you might have to improvise. But you may be able to just use inner scrapers on the outside.
Here's how the small-window cars look without the trim. I cheaped out and didn't dechrome the divider and vent trim.