340 identification

The Duster is a 71 but i already know it's an original 318 car,but the guy i bought from said that the guy he bought it from told him that it was replaced a while back with a 71 340.
The engine paint is blue i'm not sure if it's the factory paint though.

What will the casting numbers on the heads be if it is a 340?
I have a 69 340 in my Scamp but i really don't want to pull the valve cover off of it just to check the numbers.