Sorry for your inconvenience. The simple answer is yes you have bought a lemon. I mean no disrespect whatsoever saying the following. The owner may or may not have known the head gasket was shot. In any case the screw driver you found and his explanation told you immediately that " his baby....maintained every 5k etc" was a load of baloney.
A quick look here would have told you immediately what you now know the hard way. You unfortunately have been just as naive as the owner to part with the cash. But this is all hindsight now, where to from here? Again not meaning to be the Christmas grinch, Expect at least $4 to fix the first obvious problem. You may do it for less but unlikely. The next thing will be then how many more thousand you will have to throw at it to have the vehicle you were expecting. IMO for a poor maintainedD2 add another $4k without the auto trans, again, less if you can DIY. Commiserations, try have a good Christmas.

