Torque Boxes?

A frame alignment rack makes no sense unless all equipment is on board,IE;Drivetrain,interior exterior panels etc. Thats how it's done when repairing a frame that has been damaged. Generally speaking,most frame shops dont pull stuff out of the car unless needed.

Thus I think that if you had a car you were already driving and wanted more st iffness,simply weld the torque boxes and or subframe connectors in with the weight of the car on the suspension. This would make for the least amount of panel alignment/adjustment issues and will likely not affect front end wheel alignment either.