Newbie here!

So I've been reading here on how to check for rust on frame and birdcage, and it was mentioned to bring a small mirror to look through some holes on the door or door frame? Can someone please elaborate as how this procedure is done? Hold the mirror outside of the hole and look for rust, if any, that reflects back from the frame to the mirror? Where are those holes located?

Like I said I am a newbie and am learning as much as I can before buying my first C3. Thanks in advance for your help!!!

 

The birdcage starts from the windshield and goes to the frame rails.
I would inspect the chrome windshield mouldings and make sure rust is not pushing them away from the glass surface. Not much more you can do here its not your car to start taking apart.
Some rust may be observed behind the kick panels. If the seller is a wrencher he may remove at your request if he thinks your are serious about the car. Requires removal of the rocker panel trim and kick panel where speakers are nestled. Phillips screws for this one.
I had my seller put the car on a lift. I then asked for a box wrench.
He looked at me funny. I told him I'm going to probe around the box rails and see if I get a face full of rust out of the weep holes on the frame. He was good with that, he just said watch out not to wack the fiberglass. This was my second trip to see the car and he was semi confident shy of major frame issues I was buying it.
I felt around the frame as humanely possible as a buyer can looking for damage or rust. The seller is not gong to pull the body off for you to inspect. I try to look at the sellers pont of view if it was my car what lengths would I go to for a potential buyer. The holes in the rear wheel wells are what I think you maybe referring to.
These are usually tough to get at if they are all sealed up by old undercoating. If they are to be removed by the seller a brite led flash light and a mirror will allow you to observe the rear framerails that are often suspect on these old cars.
A corvette restoration book will point out common trouble spots. Also you'll know then if something has been cobbed up to cover old damage.
Look at a few cars from show to resto and pick the one at your level of comfort you want. I chose drive as I go. Mine has a 10 footer paint job and small cosmetics needed but it runs great and is safe to drive.
Keep askng questions; I still am
Marshal

 

Skip the mirror. You will probably not need it.

 

The least offensive way (to the seller) to determine if there is bad birdcage rust is.. Take a piece of newspaper, lay it down in the footwell over the floor mats, then open and close the door a few times (dont slam it real hard, but enough so if there is rust up there, it will drop flakes), inspect the paper for rust flakes. If any rust flakes make their way to the paper after that, then you know the rust is bad, if the paper is clean, then further inspection would be advised.
Rust flakes on the paper = Run away