Many thanks to all for comments and input about this (including Goggo who I have spoken to privately).
We have now heard from the owner. He thought he had ordered £1,064 worth of parts and had them delivered to us, but when my friend said we had not received them he checked his records and found that he had forgotten to place the order.
This suggests that he has done a good check of what he has, and now will order and pay for all the parts that are needed as soon as I or someone else agrees to take on the shot-blasting, repairs, shot-blasting, preparation and spraying, for perhaps around £800-£1,000.
Would welcome any more comments, as it is still a close call!