core plugs in cylinder head

finally got 2.5 n/a fitted to carawagon today, only had engine running without water to test it, started to fill up rad after two watering cans still no sign of filling up, checked around found no leaks but heard dripping inside engine, checked dipstick and found level to be right to top mostly water.My initial thoughts were head gasket gone so started to remove head and found all of the small core plugs situated under the rocker shaft blown out. anybody else had this and what's the funny brass tubular things that stand under the core plugs?

Not helpful but I don't know. Can't see them in the parts diagram. Could they just be spacers/packers to stop the core plug going in too far?

(in my manual, it says never ever run the diesel without water. Is this why?)

A couple of photo's might help

yes thats what i thought, to stop the plugs from going in to far, i have ordered some new plugs from buckley bros and they had never seen them, i have had a closer look today abd they are made of brass very thin gauge rolled into a tube, i think thats all they can be there for, thanks anyway

ref running without water it was only for about one minute