Changing out trunk pan

Eventually i will be changing out the trunk pan on my sons 69 cuda. Will be changing out rear seat/transition pan as well. Car was butchered with aluminum tubs as a drag car, will remove those and want to do a clean minitub w stock sheetmetal since the car actually has a nice spring relocation job already done to it. I have a rust free rear seat pan, and inner fenderwells, and trunk floor out of a 71 scamp. I planned on installing the rear seat pan first with the angle bracing that goes behind the seat to tie the frame together and give a place for jackstands to support it all.

My plan since i have new quarters, and will need a rear valance, trunk drop offs and outer wheel houses anyways would be to remove the old valance, remove the framerail cross tie bar behind it, drill out the spot welds and slide the old trunk pan out through the back.

I have never done this job before, but the way the metal overlaps i am thinking this is how i need to do this.

Anybody do this job like this before? I have a mind like a steel jawed trap, i wont forget this information even if i dont do this job until 5 years from now.

Thanks
Matt