For other cage specs, you should refer to Section 21 of the rulebook:
https://nationaldragster.s3.amazonaws.com/Rulebooks/2023_NHRA_Rulebook_22_11_08.pdf#page=326
My understanding is if the floor plates are bolted, then NHRA requires a top and bottom plate. If you weld the floor plates (which you should IMO), you only need one 6"x6" plate on top of the floor pan. Or the tubes can be welded to a frame outrigger connecting the frame rail to the inner rocker. That's how I did mine.
I bolted my procar seats where the stock floor doubler/stiffener plates are. If your mounts fall outside of those, I'd make some new stiffener plates with some 1/8" plate or figure out a way to tie the mounts into the frame somehow.