Well... after some more extensive digging into the chassis, I do believe mine is rusted past the point of no return. At least past the point that my budget and skill set could return it, anyhow. After cutting out the passenger floor pan, I found rust all the way up the tilted pan the goes under the rear seat hump, as well as a good portion of the underside of hump part. 2/3 rocker vertical members and the bottom of the quarter were also completely rotted from the wheel well to almost a foot forward. The driver's side isn't looking a whole lot better.
New plan: Sell of anything salvageable (suspension, diff, subframes, body panels), and start fresh with a ZX platform, as I understand they are sturdier and less prone to rust. My interest and skills are definitely more on the mechanical side of the spectrum VS body and fab work. Chock this up as a learning experience, I guess.