Finally got a chance to do my calculations...
Main belly pan
63.75" long
63 3/8" wide
+2.5" for width to account for side skirt studs
65.875" width total
48" wide x 96" long aluminum diamond plate sheet 1/8" thick
96" - 63.75 = 32.25 - 0.25" kerf = one panel at 32" x 48" and two panels at 63.75" long x 23.875" wide (48" / 2 = 24" - 0.25 kerf = 23.875" x 2 = 47.75")
65.875" - 47.75" = 18.125" wide x 32" long panels (48" - 36.25" + 0.25" kerf = 36.5" = 11.5" x 32" scrap left over)
Frame and stiffner support beams
2 slotted angle 1.25" x 72" (East/West) cut to width of crossbeams
3 aluminum 1" x 1" x 1/8" angle x 72" (North/South) cut to 63.5"
As I think about this, I may have to eventually redesign my crossbeams and how the engine bay belly pan attaches to the front crossbeam. If I rebuild the crossbeams with rubber attachment points to the truck frame, this will allow fer torsional flexing without damaging the crossbeams. I might be able to build the flex joints from conveyor belt material by stacking layers and bolting them together.
I'm also thinking about painting the inside part of the belly pan that runs along the exhaust with some high heat black paint to minimize the amount of heat being reflected back to the floorboard.