[73-stang]

I just got a 73 mustang with a 351 Cleveland, it has a cam, holly deliminator intake with a 600 holly carb, i was wanting to put new heads on it how can i tell if its a 2 valve or a 4 valve heads? Will the 4 valve heads bolt to the block? Will my intake and exhaust fit if i get 4 valve heads? Let me know what you guys think thanks!