O-ring size: Usually inner diameter x cross section (thickness)
11 x 2.5 has outer diameter 16mm.
So when change to a thicker, inner dia must be smaller to not increase outer dia too much so it still fits. Here inside the gasket holes.
Same with oil feed o-rings. The inner dia can not be too small either so it block the oil feed when compressed.
Here just a few 0.1mm to compensate for thicker gasket.
I used 8 THICK o-rings with late CB750 head gasket and early cyl/head. I had to re-torque the head 3 times until it stopped compressing, nuts moved after 24 hours!!
I used thinner viton O-rings next time (changed head), something like Hondaman recommend. Re-torqued once after 24 hours was enough. (I tested once more)