Hi and welcome.
Some pics of the car would be good but I suspect I know which one you bought (reg starts LWL
) The best way for me is to put them on photobucket then you can just cat and paste the IMG links here.
Spiders rust from the inside out as a result of not being watertight. Floor pans tend to go as do the bottom of the A & B pillars, screen surrounds and inner rear arches / turrets. You'll want to check the sills too and the special channels where the floor and sill join that are especially designed to trap water.
As far as I know there are no off the shelf floor pans unless Mark (
https://353652584127257704.weebly.com/ ) has a source. Patch repair may be possible or indeed your only option depending on how far gone they are.
If it's the car I think it is then it's a pre-facelift model, it's just my opinion but I'd want to keep the original 1970s interior if possible, it's rarer than the later type and far more distinctive. Pretty comfy too.
An hour on here will turn up lots of links for parts - but be prepared to have to get bits from all over the world.