Wel I took the rocker off and couldn't see anything untoward at all. Reset the tappets at 18 cold rather than 25 hot as by the time you strip it down and get to the last tappets its cooled considerably anyway ! Still has the damn rattle.
Used the truck and all was well ... but ... next morning it wouldn't start. Its always started first turn. Eventually stuttered into life and I then found a vacuum pipe at the rear had popped off. Next morning it started ok though not as quickly as it used to. Reckon I'll change the glow plugs before winter sets in.
As for the rattle .... that remains a mystery