The driveshaft/extra crossmember is a fantastic idea and should help give your car roll cage like rigidity with all the extra supports you have installed to shore up the flimsy unibody! I also installed the subframe connectors/ torque boxes in my Challenger without any drivetrain installed. I'm not sure how the factory did this but I am sure it will lessen any amount of frame deflection and movement once the drivetrain is installed.... My car will be put on an alignment rack and setup for optimism performance so I am sure factory specs won't work for me......