Hi Ian,
The only damage, except from mechanical damage due to the chains in the housing, is bent or damaged valves. A leakdown test, or compression test would give a definitive result.
A good and simple way to check would be to let the vehicle idle, and check to see if there is a misfire. No misfire would indicate little or no damage.
You would only need to replace chains, ramps and tensioners.
Good luck.
Markus
