True. But I'm not quite that invasive on a typical deal, especially if we're keeping the leaf springs. We use a 2x3 and section it into the rear seat floor area so it is half above the floor and half below at the rear rail area. Open up the front of the rail where it joins the floor, half above, half below the floor so the connector will slide into the front of it. The rail can still be drilled up for plug welds if you like. Section the floor so the connector will rotate up and bump into the rear of the torsion bar x-member and just touches the top flange where the floor is spot welded to it. Everything will be above the pinchweld of the rocker this way. "Outriggers" from the connector to the inside of the rocker can be installed to mount the main hoop and diagonals rather than using plates. Makes for a stiff platform.

This will take some time to layout and cut to get the connector in parallel to the CL of the car and keep the fits tight for welding. But the results are worth the time.

Wish I had taken photos of some of this stuff.