After much deliberation, I've decided on roughly which style I'm going to go for.  There were several other options, including a frame within a frame design, but I've settled on the relatively simple option even though it has the added expense of 3 cylinders instead of the 2 on the other ideas.  However, there is a potential problem in having a mechanical valve system that can perform all of the movements necessary.  I've emailed a load of hydraulic companies in the hope that they can offer some insight, but if anyone reading this has any ideas then please let me know!