I just had to replace front passenger side floor and a portion of the foot riser panel. I used a flat piece of 18 ga metal for the floorpan and cut out two large round holes at the location of the floor-to-frame bolts. Wrapped a piece of metal around the hole and welded a washer at the bottom to make up the recess for the bolt head. I did not do the stiffener recesses (since nobody ever uses the passenger side anyway) and also I did not overlap my floor panel over a portion of the old floor. I elected to weld it on flush with the existing floor using temporary fitting tabs in some places and permanent ones in other places underneath.
I intend to show photo's of the project including inner & outer rocker panel cutouts & repair, rear wheelhouse rust cutout and rebuilding, rear quarter panel cutoff and replacement, rear of trunk floor and tailpan rustout cutout and repair at a later time.
Like you, I also have only crude hand tools (hand shears, old jigsaw with a metal-cutting blade, hammer and mig welding outfit).