They are talking about the casting numbers found on the head. The "302" refurs to the last 3 numbers on the heads casting I.D. numbers.
These numbers are found in 2 places. On the intake runners under the head or ontop of the intake runners under the valve cover.
Sometimes you will see someone say the have a head that gets I.D.ed as a letter. Examples are, X, J, O etc...
These are earlier heads but also have a casting number. X and early J heads have the same casting numbers ending in 915.