Re: just wondering
There are several different variations of the GT40 heads. Here they are...
F3ZE and F4ZE casting #'s = 60-63 cc
F1ZE = 63-66 cc
F77E = 58-61 cc (GT40p)
The F1ZEs were the earliest model of the head and were used in marine applications originally. You probably want to avoid them.
The Explorers came with the F37E from 96-mid 97. These are the same heads as the 93 Cobra. Then they switched over to the F77E (GT40-Ps).