steel and aluminum are both metal

yeah I have about 1/4" of good metal with only a few small holes in it, after the curve down from the sill plate under the doors. i still have some of the pinch seam at the very front of the floor pans, and a bit at the back. I have pics I will have to find and Ill include them.

Looks like a prime candidate for the 2X6" rectangular tubing replacement to me. I wish I had done that in retrospect, it would've been simpler than all the bending and it looks nice.

I was running with the pop rivet and seam sealer idea since it was a lot cheaper, but I really don't trust how long my job would last before potentially rusting out/get damaged. your idea is much more appealing than when I first considered it.

I have seen some good write-ups, would it be quite easy to join my new floor to a new 2x6" rocker? I have access to a welder and a person that will do a good job if needed.

I didn't do mine that way, with the 2X6" tube. Should've though. Hopefully someone who has can answer your question.
My floor repair attached to the existing metal under the plastic trim along the door sill and to the trans tunnel on the opposite side.

Its as easy as joining a thin sheet metal to a thick wall tube, but I dont think you cut all the rocker away. If there is still rocker on the inside I'd try and leave it.

I patched mine with sheet metal, Goop, sheet metal screws, coat of rust paint and poor man's Dynamat, the roofing sealer strips that are available at the local Lowes or Homedepot. Big issue is making sure that you seal it well so that no carbon monoxide from the exhaust can get in.
Water, mus or the rest of the crap that you can float in isn't the dangerous stuff, it is the stuff you can't see!
Adding the sealing strips sure cut down on the noise and heat as well.