I have finally managed to take a good look at what I bought. Sold as a part-complete Waverider, it is, but in any useable way. I suspect the seller had picked it up at a clearance or car-boot sale. It looks as if everything is there, but the keel & frames that had been assembled are useless as the ply has delaminated. Luckily, the powder and water glue supplied with the kit (probably Cascamite) hadn't done too well and the parts came apart with a little gentle persuasion. They can be used as templates, at least.
The rest of kit, in its box (price on the front 69/11!) has obviously been stored somewhere better than the assembled parts. I have now vacuumed away the loose powdered glue - everything had simply been tipped into a cardboard box and posted, no protection at all.
I now have a reasonable kit including plans for a Waverider, and will be building it, using a lighter construction than the original 3/4" ply keel assembly!