No one knows where to check 57, 58 for frame rot?

[Pontiac59]

Looking at picking up a '57 Special convertible to flip and possibly a '57 Century 2dr ht to make a package with. Both have sat outside for years.

Where do I check them for rot? The Special I have a feeling the bumper and frame stub that sits on it's hood, is it's rear bumper. But it would mostly be a parts donor - all the convertible stuff seems to be intact. I just mostly need to know where to look under it to be sure it won't break in half, or know if it will so I can take it apart some first and try to minimize the damage. Looks like someone stripped and repainted it, of the half-dozen or so of these I have seen in yards only the one someone had purposely stripped parts of, had big bare rust spots showing (unless the factory light yellow didn't hold up as well as other colors).

The Century the body, rockers and floors look good on, but I have not been able to check the frame. Someone pulled the carpets and the seat and I didn't even see a hole under the gas pedal. It's really cheap, so I am not super worried, but if the frame is weak it will be no good for building a convertible with. I pulled glass from a car near it last summer and got my first ever dose of poison ivy, so I want to spend a minimum of time trying to poke under it with a flashlight.

There is a third option, too, a friend has another '57 - a Special 4dr. I might check it out because the motor in it is supposed to turn over. Same deal though, another old New York car.

Last but not least I know of a cheap '58 4dr, minor damage to the front right corner but complete and apparently a runner that was on the road maybe 10 years ago. Any special places those like to rust? I think I can find the parts to put it together if someone wanted.

Incedentally, when I mean rot, I mean how to check cars that saw winter duty in road salt conditions, odds are none of these have been bondo'ed back into shape or anything like that. For the most part cars lasted 10-15 years and then people junked them, up here. Your 57-59 Mopars have areas in the frames they like to rot, your 59-60 GM X-frames I can tell the single exhaust cars because usually the side with no pipe no longer has a trunk pan or a frame rail left, stuff like that.