Update
Quick update.
We couldn't find a suitable and cheap engine so we took deep breath and dismantled the whole lot fearing the worse given the blown out injectors.
We were pleasantly surprised given that the fuel injectors had blown out and after very careful dismantling and inspection the bores and other crucial bits have survived.
The upshot is a re-machined block for the injectors to go into, new clamps and a complete rebuild which is taking time but is a hell of a lot cheaper than the other options available.
Can't say enough about the specialist Autotech in Carlisle who have held my hand all the way through and have taken a great deal of care and proffered well though out advice all along the way - despite the fact that my car had been tying up ramp space for the last 5 weeks whilst various breakers yards fannied us around with broken promises and duff engines. They are fitting in my car with all of their programmed jobs so it's taking time but the job is getting done properly and not being rushed.
With luck I'll be able to drive the car for the second time within the week - I've budgeted for around 30 hours all told plus machining, oil, some parts (head gasket, clamps) and vat.
Lesson learned and bizarrely I kind of feel like I've got way with it - how strange is that?
I'll report back when the bill needs to be paid...