floor pans
Easiest is a full pan that goes all the way to the frame rails. Hardest is cutting away part and fitting the new metal to the hole w/ no gaps so you can butt-weld them, especially on the curved tranny tunnel. I did the later, and actually got them butted well after ~10 passes. But, only my 3rd time w/ the cheap HF no-gas flux wire welder, and I got more than a few burn-thru holes. Holding a copper spoon on the backside didn't help much, and hard to do so (magnets). I had to add steel wire filler in places to repair. If I did again, I would overlap ~1/8", making the fitting much easier and also avoid burn-thrus. Nobody will see it under the carpet and I couldn't clean up the underside well anyway above the tranny x-member where you can't access.
Other hints - clean rust and paint the front frame rails and cross-member while they are exposed. I sprayed, then ran a rag soaked in primer (Rust Destroyer) thru them several times. Use "weld-thru" primer anywhere metal will be trapped after welding. High-zinc spray at hardware stores works.