Undercarriage Question

It's been years since I've worked on a car of any make/model and most of my knowledge comes from reading the Hayes/Chilton/Service manuals. My Dad was a bit sexist when it came to car repair instructions.
I've got all 3 books for my 68 Valiant and can't find the answers. There's repair instructions all the way down to the seat floor panels themselves but nothing under that. The floor panels feel solid for the inside.

Ive got a piece of what looks like it used to be sheet metal but is rusting out bad, reminds me of Pillsbury Grand Biscuits with all the flaky layers.
Do these cars have (or supposed to have) a undercarriage panel(s) covering all the parts?

I can't afford to take it somewhere to have it looked at yet, and it can't go anywhere until I get the brakes doe, gas tank installed, and new tires on it.

I can get pics if needed.

Links and pics welcome! Thanks in advance.