The spartan board is a combined trigger board/fcu/wire harness, it's v2 only and is used to save money and space for those guns that are compatible.
It's an all or nothing deal, you either use the spartan or you need separate trigger board, fcu and wire harness. So yes it would replace the spartan.
I'm assuming that the Gorilla FCU includes it's own branded trigger board (which is probably much better than wolverine's), and that you are using v2 gun.
Spartan Edition + gorilla fcu package : you would need to buy a wire harness, then maybe sell the spartan board.
Premium Edition + gorilla fcu package : wouldn't need to buy anything extra, but you will have a trigger board and expensive premium fcu that you don't need. Could sell them.
Spartan or Premium edition, it often comes down to what is available. It can sometimes be difficult to find stock of the individual parts such as nozzles and trigger boards.
If it's not an m4, it's always worth checking the chart in case you need a different nozzle
https://www.wolverineairsoft.com/compatibility/