Jim...that is a shame. Don't think you can go after the surveyor...but with the testimony of a marine diesel guy, perhaps you could get a small claims court redress with the owner for some of the cost of the damage. The key issue will be "did the prior owner know". You said you went on sea trial and found no issues so it is possible that the owner did not know if the engine performed properly on trial.
I generally advise against turbo models due to the added complexity and parts. I would think 54hp is plenty even for a moderately heavy 43 footer. Why do you feel you need the additional HP?
Finally...for others reading....ALWAYS get a separate survey of the diesel engine on a boat and arrange for the mechanic to accompany the boat on sea trial and put the engine through its' paces. Regular surveyor are generally not equipped to evaluate anything other than GROSS engine issues. A few hundred extra for a qualified diesel guy can save thousands of $$'s
No longer posting. Reach me by PM!