hi, good for you, doing research before you buy! Let me explain as best I can, the Eagle/AMC unibody. OK, start with the floor pan, ok picture it, stamped sheet metal. Then add rear and front inner fenders, also sheet metal. To mate the two you use a subframe, kind of like an open channel. The floor pan slides into the front subframe channel, while at the same time the inner fender sheet metal slides up to it. You have now three layers of sheet metal spot welded together. Now, this front "frame" is unlike regular frame section box steel, it is both angled a certain way, an tapers a certain way. It is not easily fixed with a new section of box steel as , say, a Jeep frame. Originally this was a great idea. The unibody was VERY strong, while doing away with the weight of box section steel. The problem now, is, that in time these layers separate, if only a little, and moisture gets in there, and rust starts, and never sleeps. I know what I am doing, and I can still get fooled. My current Eagle project, an 84 sedan. Before I bought it I crawled ALL around and UNDER it with a flashlight and a hammer, looking for soft spots. Didn't find any. Fast forward a couple of years, took motor out saw a SMALL spot of rust on inner fender, investigate further, and about 80% of rail is rotten from the INSIDE. When shopping for an Eagle, run your hand under the upper control arm, this is a place you can't see, so feel with your fingers, if it is rusted THROUGH, even a little, that frame rail is on it's way out, maybe good for another 5-10 years, but on it's way out. This is not meant to discourage you, just a heads up. The AMC Eagle is a truly unique car, and worth spending some money on. As I have said, cost me $750 to have that left front rail fixed. shop carefully, and good luck, gz ps having said that, my last Eagle, an 82 Ltd, ran for over twenty years while slowly rusting out, I fixed the floor once ten years ago with fiberglass matt and POR 15, kept it together for ten years. It is now too far gone to save, but, well, it was our daily driver for TWENTY ONE years. A good Eagle is hard to kill!