Thanks for that – I'm getting an idea now of how to proceed. I've got a pretty good indication of construction from the pictures on Michael J King's website and I'm thinking Sycamore and Spruce might be the right materials – the former should be resilient enough to take psaltery/zither tuning pegs and both are readily available. The idea of frets seems like a good idea and would mean the bridge will be at right angles to the strings rather than at an acute angle (presumably this made it easier for the bridge to rest on the face and back). Obviously, this will mean revising the soundhole positioning.

I'll have to draw up some plans and experiment a bit. I reckon this is going to be my winter project. No doubt the quiet peace of the RIV will be disturbed by loud and inventive expletives as I get it wrong.