Reinforcements for whole floor removal

Hi everyone. Over the winter I'm overhauling my '69 Barracuda notch. I'm getting ready to replace the floor pan with a whole pan from AMD. I've heard that it's important to brace the body when removing the floor pan. I've seen that some people jack up the car at various points, which I'd rather not do because my garage is small and it's helpful to be able to roll the car back and forth. I've also seen a method that involves welding steel bars on as temporary reinforcements.

This seems good to me, and I have two pieces of 1" x 6' box iron ready for this purpose. I'm trying to determine which would be a spotter spot to weld it:

1. From a spot on the metal behind the rear door panel (around the rear window crank area) to a spot in from of the door behind the plastic kick panel.

or

2. Connecting the frame rail below the rear seat to the frame rail by/on the rear transmission mount - or even further ahead too (I have 6ft). Potentially, I could scrounge up another piece of metal to join the two braces, creating an "H" under the car.

I favor the latter approach, but wanted some more experienced input. My car is fairly original, and the door jamb paint is in great shape, so I'd rather not weld to it. The frame rails area is easier to weld too and won't be in my way as much when I'm working, but I want to make sure it will provide the necessary reinforcement.