Pouring the tranny sounds like a good way to go...the soft spot in the floor sounds like a candidate for the Git-Rot repair...a 12" x 24" area?...it requires drilling 1/8" holes on 2" or so centers in the thoughs of the non-slip pattern in the soft area...allow the core to DRY THOROUGHLY and then inject Git-Rot into the holes...it'll set up , then do small gelcoat dabs on each hole and yer done...Google up Git-Rot and rearch the exact hole placement...it may be the way to go...good luck either way ya choose, give us pictures as ya go...
