I believe the 1978 512 uses Ishiwata 022 which is 0.9 - 0.6 - 0.9 double-butted chromoly, which is pretty decent stuff. Like JunkYardBike says, if the frame is straight without any dents or rust, I'd grab it.

EDIT - I just saw where JunkYardBike thinks it's a 712 with Reynolds 531. If so, that makes it even more desirable.