engine mileage

[pirana2671]

As long as nobody tried to limp the car anyplace after blowing the head gasket you should be fine with just replacing it and having the head checked at a machine shop.. If they did try to limp it home and the head gasket was badly blown, you can expect the possibility of much more work, I.E., wiped bearings if water got in the oil, possible cylinder damage, But until you pull it apart you won't know.

As far as how long they will last, well that depends on how well they are maintained; mainly oil change, coolant change and basic tuneup. Either way you got it for free so go into it with the thought that it's an interesting project.