For those playing along at home i went and looked at this again today (mostly cause i wanted to play it) but when i lifted the playfield the cab speaker clearly said 4 ohm.
I also saw the dangling 4 pin connector that was hiding.
While i wasn't looking some moron (probs a big stupid tattooed bastard) went and disconnected the sepakers from the sound board.
Plugged in and the new 4 ohm is talking to the old 4 ohm and all is good. Just need to mount the new cab speaker now, but it looks like it will need some sort of spacer.