sort of off topic, but same sort of story, my son has a 20 year old TVR. he has had it for 7 years or so and knows the car well and does all his own servicing etc. It passed a good mot all ok, but he decided to rebuild the whole car recently. He want to keep it forever! This meant taking the body off to reveal the chassis.
The four corners (the bits you cant see or get to with the body on) were all rotten, almost hanging off! And this is on a well cared for car. I have seen a couple more similar TVRs now, I would now say any 15 year old or more TVR is the same.
The reality is so many cars get a nice top polish, and people think that if you have something sitting in cold wet English weather for 50 years it wont be rusty! These cars are all pre-galvanised steel so unless they were kept in a bubble for the last 50 years I cant believe they wont be rusty. My 66 230 has had 2 complete floors in its life time, last one around 7 years ago, and this was a one owner - kept in a dry underground garage in London.
Shame is most people only look at the top shinny paint!
I guess its buyer beware all the way! Good luck on the project, looks like fun!