I thought of using one of these, saw it in harbor freight for under ten bucks, it is call a contour gauge. Thought about using it to get the shape of a section of the floor from underneath, transfer it to cardboard to make a template, then another section of floor and transfer to template, until I have the whole floor section, frame rail end to frame rail end. then transfer the template to the steel and cut it out...viola homemade sub frame connectors and they are custom fit for your car.......or so it seems to be a valid idea...