Re: If you really want to go off-piste ...
re: hydraulic computers, there was MONIAC but I'm not sure if it counts as hydraulic (involving water pressure in some useful way) or a computer in the usual sense.
What prompted me to reply, though, was that I just recently came across the idea of a hydraulic ram pump. Sounds like it would make an excellent component in this speculative machine.
Now you've got me thinking about powering stuff with water in Minecraft :(