Oh well. It followed me home.
Turns out when he said he'd "had it running recently" - that was a few years ago!
Checked it over, all things move as they should, new gapped plug, freed up stuck float valve (flooding) and tutu with the governor mech (which still needs work), un-tutu'd the dead-spark wiring, made a crank handle and spun her up, she's alive!
I might even get to posting a video oneday.
Will have to either tear into it to fix existing throttle arrangement, or just add a lawnmower type cable/friction lever. Will put it under load and see what she does.