So why have all the water gallerys/holes in the head and barrel and then some not in the head gasket or so small in comparison 
Must be a reason but its escaping me at the moment 
The smaller holes are to slow down the passage of the coolant, giving it more time to soak up the heat from the castings.
Earlier gaskets more closely matched the castings, but experience from racing proved that they weren’t completely necessary, as time went by the holes got smaller and smaller.
The best ones to use are as late as possible OEM or Cometic ones from the States, the factory race team back in the days of the 955/996’s all used Cometic gaskets.
It was these gaskets that pioneered the smaller holes.
Cometic can/will supply any thickness that you need to make sure that you can set the squish correctly (they also supply base gaskets/shims to set the squish), I set up my road engines with 0.9mm squish clearance.
Anything over 1mm and the squish isn’t actually working period, when you get down to 0.75mm you’re pushing the envelope as to reliability/as in the piston hitting the heads at high revs.
Titanium rods stretch in use but the go back to where they were originally (they’ve got a good memory), it’s for this reason that I prefer to use Carillo Steel rods, they’re lighter and stronger than OEM rods and don’t stretch in use anywhere near as much as Titanium rods.
Factory Corse 888/926’s used Carillo rods as standard.
Steve R
OK makes sense 