Originally Posted by Marki_GSA
There has to be some access otherwise you wouldn't be a able to build the engine in the first place. Of course they could be 3D printing them. ;)
This is educated conjecture at its best, but the design looks like a wet liner design. It's likely that the block is assembled with the rods attached to the crankshaft. The pistons would then be installed into the bores of the liners. With the pistons protruding from the bottom of the liners the piston wrist pins would then pushed through the pistons and into the upper rod bores via an access hole made available through a water pipe flange, or some such, on either cylinder when the pistons are joined with the rods.
This type of design was used by VW on the Wasser Boxer Vanagon for many years. IIRC, Renault was also fond of this design. A major drawback of this design is that removing the piston pins after many miles/years of use is difficult when there are some carbon deposits on the exposed portions of the wrist pins between the upper rod journals and the piston wrist pin bosses. Special tools are usually required to facilitate pin removal. Neanderthal measures and home mechanic clubbings don't work here. An owner of this type of engine design must not neglect or lengthen oil change intervals and must not use inferior dino oil.
Another drawback of this type of design is that the o-rings at the top and bottom of the liners are also sensitive to poor maintenance. The coolant must not be allowed to degrade enough to allow corrosion of the grooves that hold the o-rings. Without proper maintenance, the o-ring grooves degrade and cause the o-rings to fail if the liners are made of iron that is exposed to the coolant. This would likely allow water into the crankcase and its oil if the liners aren't coated to protect the iron in the liners or the liners are not made of non-corrosive materials. Electrolysis is the enemy here.
The rear view of the block doesn't show any access ports, water pumps or flanges that might provide wrist pin access. I would bet that a frontal view of the block would provide evidence of properly positioned devices that allow access to the wrist pins. Such a view would solidify the idea that these engines are a wet liner design.
This is my take after rebuilding many Vanagons and is subject to withdrawal after serious internet flaming or real proof otherwise avails itself.
As ever, YMMV.