Hi
I always thought it was hand built when I could see no labels on it and you informed us quite early on that you had no information.
The pressure gauge might well have a much larger scale than the press or the cylinder can take, unless you can talk to someone and find out what sort of pressure was generated during use or if it is fitted with a pressure relief valve for which you might find the pressure relief setting. I think your stuck with starting with dimensions and trying to identify material grades or assuming the lowest grade materials.
That said I would be concerned about the hydraulic cylinder if it as not been constructed to a design code.