Like the fellow said, they will bolt in place.
A few minor things...
You'll need the earlier perimter bolt valve covers to match the heads. Obviously, the center bolt one won't work.
There likely won't be a threaded port in the earlier heads for the temperature sending unit that the late model engine will have. It depends on the age of the heads. Even if it does have the threaded hole, it will be the wrong size. They went to a smaller hole in the early 80's. From 1/2 NPT to 3/8 if I remember correctly. The point is, you'll have to figure out another place to mount your temp sending unit.
Lastly, any accesory drive brackets won't work. The early heads don't have the tapped holes in the ends for the brackets to screw into like a later model application uses.
