Right, it arrived today.
Put some bullet connectors on it, and plugged it in to the feeds on my engine. Yellow to yellow, White from the stator coil to pink on the rectifier. Black from stator to engine earth. And then red to be wired to the battery. I put a sheathed female bullet on the green, and for the moment it is not connected to anything.
Turned the engine on the pull cord, and sure enough generated a dc voltage (1.5v) on my multimeter across red and earth. Looking good, and next weekend the engine will go back on the boat and then I will find out if it actually works!