Can you mount the front z28 chin spoiler on berlinetta front bumper. How hard is it?

Why not? It's simply a cosmetic attachment. It won't have the same effect unless you also have the ground effects.

the berlinetta and z-28 used different nose pieces. the outer corner is different between the 2.

Correct. You will need to change the whole front nose. Also the nose and chin spoiler are year specific. 82-84, 85-90, 91-92. The whole front can be exchanged between all years, with some minor drilling for attachment points. Hope this helps, Dean