thanks gentlemen, much appreciated
Answers:
The neck and body fit well.
None of the four neck-holes align with the six body-holes.
However, the four holes in the neck are at the same distance from the centreline (and presumably the trussrod) as the six holes in the body, so I am not too worried about that.
This popped up today on eBay, so that might clarify the origin of the body.
http://www.ebay.co.uk/itm/Vintage-1960-s-Kay-Precision-Bass-Guitar-KB24-Neck-Plate-/261108965007?pt=UK_Musical_Instruments_Guitars_CV&hash=item3ccb4e9e8f
I'll update when I have more.