I have put 14,000 miles in three years on an original 260 that came to me showing 34,000 miles on the clock. There were issues with the said clock and I would not be surprised if it had been disconnected for periods in the past: the dial was rebuilt but the cable not corrected so it was failing again when I got the car. This car has never been put away for any period beyond a yearly winterization.
Anyways… the car came to me with seeping original head gaskets so I had to remove the heads. The valve assembly was dismantled, the carbon cleaned out everywhere, the valve seats polished using the original valves. Everything looked ship shape, no pitting or surprises anywhere.
The car runs great with unleaded.
Cheers, Gilles