I have just done a quick measurement through the packaging and the prop is three bladed and about 2" in diameter with a 4mm prop shaft. So what I will need is a nice big torquey motor either with a reduction gear or without. Which should be easy and cheap enough to find.
I can well believe though that Powerperm and Decaperm are one and the same as this is a German manufactured kit and probably originates from about ten or fifteen years ago. It is still available from the main mail order firms at anything from £415 to £460. So I am well pleased with it.