Subframe connectors for a driver/cruiser, necessary to weld to floor?

There's no guessing on 50+ year old rusted sheet metal. I run street radials on my 4-speed '69 Dart. Engine is a built 418. My 1/4's are flexing. The car has the factory torque boxes and home made subframe connectors, also 4-link coil over rear suspension. I know that it will be a lot of work winter project, but the old torque boxes and sub frame connector are coming out and will be installing the uscartool torque boxes and sub frame connectors.
I really don't want to put a roll cage in.
So all advice here is good, but every car has its own weaknesses.
Good luck with what you do.