Subframe connectors

So you are recommending to literally stiffen a bow into the car? You "May" have done it however saying as long as the doors shut its ok.......... that sounds like a fairly agricultural build theory. Not sure why you would risk it given how simple it is to load the wheels up. Big difference between a door closing and a door with a perfect panel gap.
Do you really think the bodies on these cars haven't sagged between the front and rear subframes over the last 50-60 years? This is an instance that people tend to overthink in my opinion. It's obviously been done both ways with great success. Pick one and go with it. If the panels align well and the doors shut well, burn them in. It's not worth losing any sleep or arguing over really.