how to identify

3 vertical bars on the front of the cylinder head denotes a GT40 head.
4 vertical bars on the front of the cylinder head denotes a GT40P head
You can also look down by the lower head bolt on the corners and see if it has GT or GT40P or GTP cast into the head.

The GT casting is a GT40 head while ones marked with GT40P or GTP are GT40P heads. If you don't see any of these markings then more than likely you have the E7 heads.

A 91 cop car has E7 heads, they didn't get any special treatment to the long block...they were all the same.