I think that on a US market car, you are not going to have a GF block. We are told that at some point after that, for cars built in the late '70s or '80s, the supply of US 4v Clevelands was exhausted.
Those cars are built in such small numbers that there really isn't a definitive answer but it was suggested that Detomaso obtained the engines from Ford of Australia. That would open the door to a GF cast block as well as all other components. So a GF block could have some value on a late car?
A matching engine number on a US market car doesn't guaranty that it is original to the car. A current owner can fake that to make it look original.