Yep, it's the #10 in the first picture: they were 11x2.4 at the early engines, then went to 11x2.5 in the K2. Most gasket sets, if they supply them at all, have 11x2.5, in my experience (even the Vesrah kits). The ones I send out are 10.8x2.6 to make up for the too-thick head gaskets.
Part of the confusion out there involves the now-silent O-ring change between the K1 and K2, as some savvy builders working on the K0/1 engines measure the original one (2.4 thick) and then step up to the first available size of 2.5mm: but, that only worked before 1996 when the head gaskets got thicker. So, that old lore is still floating around. Today, it takes the 2.6 thickness, plus a reduction of the diameter from 11.0 to 10.8 to fit in the recess of the cylinders.