Lazy cam follower

Looks like the source of all the tapping was a lazy cam follower.
All the valve train gear is in remarkably great condition given the age/mileage of the engine.

We've checked all the rockers, lifters, push rods valve seats, guide and the camshaft and nothing is overly worn. Decided to clean out and refit the followers.

Restarted it last night - god awful clatter for about 10 seconds then the followers pumped up with oil pressure and things were much better. I used a mechanics stethoscope to have a listen to the rocker covers and there's a massive difference. The engine is quite and all I can hear is the faint (normal) tapping of the valves. Oil pressure is much better now too. There is still a minor tapping which I think is an exhaust manifold - got a set on order.

The reassembly went well with the exception of one water hose that was a bit loose causing a minor water leak.

Tonight I'm going to replace the oil pressure sender and do a full oil change. Also going to try and get the motorbike up and running and ready for sale.