Oh, I saw a picture online that showed a bar going through the centre of the workpiece when fitted to the lathe ... more than one way to skin a cat then.
Sort of, more by luck than judgement, I heated most pieces just to aid bending so it sort of got annealed. Yes, you described exactly what I did.
Just a little bigger than what was required, perhaps 3cms bigger.
Unfortunately I'll be in Bristol this coming Saturday but there are others listed so hopefully I can make one of those.
If anyone's interested I'll post a picture of what I've built so far?