Thanks Everyone! I looked at the car on Saturday, and rather quicly determined it was going to need a lot more work than I was prepared for at this time. The oil seemed to be leaking from multiple sources and probably needs a rebuild.
For being in "original" condition it was in suprisingly good shape however. Everything except the windows works on the interior (one stuck up, one stuck down). The undercarriage is another story, extensive rust there, including holes in the exhaust.
I checked the VIN and it does have the 428, it's a "81 = Thunderbird 2-door Town Hardtop (1966, no rear quarter window, steel roof)" and was assembled in Michigan.
Here's the classified ad in case anybody is interested.....
http://chicago.craigslist.org/car/123108158.html
He's really desparate to sell!
It's in Woodstock IL, about 1.5 h NW of Chicago.