I have this set hopefully winging its way over to me as we speak. I was aware of the 3 individual Kings in the Superior Wizards & Lizards 25mm line (starting later on in the scheme of things at Wl-131 Oriental Wizard) however have never seen this set piece before. Superior went on to become Perth Pewter who have most of the old pieces by those sculpting greats Ray Lamb, Ron Spicer and Steve Tofano (there is also a set of initials in a listing that I don't recognise; LC - it may be James Lane Casey - please let me know if you know!). The Superior lines are listed and (mostly) illustrated on the Lost Minis WIKI here. An interesting (and growing) pdf early history of the military side Superior is worth a read over at Alnavco here.
Note - just found this set with added sheep & shepherd at Perth Pewter here.