The 8V and 16V Vits that I've looked at have been violet/white as well. I would have thoughyt that the X90 would have a J1962 (OBD2 style) connector.
I'm not sure what connector this one came with as I bought the engine, loom & ECU and fitted to my vehicle. The engine had been fitted to another vehicle previously and the wiring loom was a little butchered from that. Hence my loom has no connector at all. I'll be going with your suggestion and sourcing a OBD2 style connector.
I need to pull the loom from the vehicle again and trace some wires. I have a couple floating around in there that are connected to nothing, I suspect the "M" wire is one of those.
I just read another post on there (though it refers to a Swift GTi) and it mentioned violet with white trace for the "M" wire. I am sure that I saw one that colour, perhaps the colour convention is consistant between some models?