Yes, just to expand a little in case the point was missed. The way these parts are designed is so that the cylinder head always hits the front of the gearbox shell. This means that all the impact force from the piston is transferred through those two surfaces (cylinder head and front of gearbox shell). The pins were added after, when the cylinder head was already snug against the front, to stop the cylinder head from rotating. If you move the cylinder head back a bit, it will no longer meet the front of the gearbox shell causing the cylinder head to try and move forward every time the piston hits it. When it does this, it will be stopped by the alignment pins which means they will now be taking the entire force of the piston since there is nothing else to stop the cylinder head anymore. Make sense?