OK, things have moved along pretty smartly and the Kolstein is now GONE.
I was contacted by a long-time lurker, a pro bassist who prefers to keep a very low profile so I'll mention neither his name nor that of his luthier, and his plan is to do as near a complete restoration to original as possible. He can then consider what mods - if any - he wants to make.
I've given him the bass (as in no money changing hands, although he did offer) on the agreement that he'll keep a photographic record of his work, what he discovers, what needs to be done.
Since he doesn't post here, the plan is that he'll send his photos to me, and I'll post them here.
Sad to relate, his very first photo is desperately unhelpful ...
I had no idea that chunk/shard/splinter was missing and Thwaites didn't mention it when they inspected the bass. ☹️
I can only assume that it went 'ping' at the gig and was swept up by the cleaners the next next morning.
Ah well ...