Naw, you don't want it for $400. PS send me the lady's name and phone number.
It's a no brainer. Your proverbial gift horse. You can look in it's mouth later.
First things first, tires and brakes so you can safely get her home.
Pretty long list on what to check for. Watch the forums and you will catch on. Some of the biggies are rear end separation, bad axles, rotten floor. Most everything else is just yank the old thingy out and zip the new one in. But if you keep her be prepared to spend twice the $ you think you will. But, at $400 you can make a few bucks if you decide not to do the work. You can't buy a storage shed for near that, and it is probably worth more as scrap.
Sail on silver girl. Sail on by. Your time has come to shine.