You don't have a chassis. You have a hydro formed front sub frame fabricated out of 8 gauge metal and a Monocoque body (trade marked as Uni-body) fabricated out of 18, 16, and some 14 gauge steel sheet metal. Because GM expected (it was built into the design) to be recycled as a refrigerator or washer from Japan by the end of it's seventh year there are lots of nooks and crannies to hold dirt and moisture with unprotected (no paint or corrosion protection) crevices in the body to promote rust.
Some cars like the Vega rusted out before the seven years were up, others like tri five Chevys seemed to last forever. The factory was required to deliver a "Durable Goods" product to the public and the seven year life span was dictated by the IRS under their depreciation schedule. They couldn't use a timer with a satchel charge of C4, but they could let corrosion do their bidding. It is only because this car was protected from the weather by a previous owner that you have it today, or it lived in the desert south west of this country were there is no water required to form rust. Other wise it would be rotted out by now along with the tens of thousands of the same model built that year.
You can check for hidden rust hiding beneath "Bondo" fiberglass body filler with a refrigerator magnet. If it wont stick to shinny fresh paint it is probably rusted out there. Remember water runs down hill so look to below the belt line, or were you get a lot of splash off the wheels throwing up salt water brine if it is a north eastern car for rust.
Takes a pretty hard impact to crack the front sub frame and the captured nut cages that the sub-frame bolts to the body would be greatly deformed under such an impact; becoming so called "hidden damage". You need only put the car on a lift to reveal bent metal.