What they said. You're right that it's not a strong design, and it does wallow around in the wind and body flex a lot while driving. But even with that, thousands of Broncos have been driven many thousands of miles at speed with the top and doors off, even without bikini tops, with no ill effects that were noted.
The doors do support, but they also are just in the way when the windshield is bouncing around a bit and any new paint on either can be subject to chipping. It's just going to move whether the doors are there or not.
The bikini tops offer stability of sorts, but they also put a lot of rearward pull on the frame. If no doors, no problem. But if you leave the doors on this pull will also result in the frame pulling backward into the top of the door window frames.
Again though, many miles spent this way with only a little bit of scuffed paint to show for it.
Most of those miles may have been spent when things were newer of course, so 40-50 years down the road things like the windshield hinge may be slightly more compromised. Rust will take away much of the lower support that a new cowl used to give the windshield too. Lots of things can change.
The braces to the roll bar are best. If you have a cage, great. But if you only have a rear bar you just need to make the braces longer. BC used to have a brace kit for rear bars, while we have a nice kit for a cage.
But every rig is different, so you may have to create your own sometimes.
Good luck.
Paul
