Body panels move on all cars when jacking or driving. According to A.O. Smith engineering, a typical full sized GM body flexes up to 4" from one corner to another during normal driving. Yes, that's four inches!
If you jack the Firebird at the rear of the frame stub, the top of the fender-to-door gap widens and the bottom of the gap narrows. Not a lot, but it is enough that the door may hit the fender if opened when jacked up like this.
Same on my GTO--when jacking the frame under center of the door, the front fender-to-door gaps behave like the firebird. The rear of the door gap widens on top, narrows on the bottom.
The movement is minimized on any car if you jack near the front or rear suspension locations.
