can you double check that model number?
my information only covers a GPX30/40/50E series
nothing like you said
but in that GPX information it does not break down the cylinder in any pictorial form, it just shows how to remove the cylinder and take the crosshead pieces off.
In the description it speaks of dissassembly and reassembly in detail and mentions the flow control valve which is in the base of the cylinder rod, it says to position it with the arrow pointing towards the piston.