Just look how clean everything is inside the rocker cover! I don't know if you are old enough to remember say Ford X/flow push rod engines in their day but everything would have been caked in black clag, the tappets would have needed constant adjustment and would still be noisy because of indented rockers, you would have to remove them to remove the indents on an oilstone and in doing so would see how worn the rocker shaft was, you would then refit it upside down to gain a few more thousand miles wear, this would be on engines that had covered 30K miles upwards sometimes even less.
By 80k if you were able to nurse the engine to that stratospheric mileage you would no longer need to adjust the tappets, you could no longer hear them for big end knock, main bearing rumble, timing chain rattle and piston slap!!
You would also hav had to decoke the engine at least twice to get to that mileage.
If you look at the picture showing the old belt on the pulley with the valve gear behind, if you crop out the parts of the photo showing the corrosion on the alternator body you would say that engine was less than 12 months old and had done less than 1000 miles, or at least thats what a Ford, BL etc engine of the day would have done to have looked like that.
In my experience all Jap engines since the mid 70's look like that internally even when they have never had an oil change, just think how good the sealing must have been around the timing belt covers for the belt and especially the cam pulley to remain like that.