The fourth position in a Ford casting is a "group" ID. Z is factory replacement and E is "engine group" (original part).
F1ZZ and F1ZE should be the same head.
F - '90s
1 - 1st year of 90's
Z - Mustang
'91 Mustang cylinder head.
This might help.
https://www.enginelabs.com/engine-te...sting-numbers/