With much thanks to Jon @Bassassin for all his advice, knowledge and patience.  I've had the hots for one of the old, better quality Japanese 'SG' style basses for a while and this one popped up for sale on Reverb at a reasonable price.  A Fujigen made, Antoria branded, short scale EB-3 copy finished in what I guess you'd describe as a dark walnut lacquer.  It arrived a couple of weeks ago now.  A serial number on the back of the front pickup dates that, at least, to 4th August 1972