The ironworkers I've been around were built of heavy Plate. The structure has to be significantly stronger (actually designing for stiffness here) than the press tonnage at hand.
Also there are very large pins/bushings for the pivot points. Attention must be paid on how the load is transferred to the punch & dies without side-loading or misaligning them.
I think it could be done, I have seen smaller mobile punching stations built that are rolled on-site for the lighter end of structural steel fabrication.
Thinking hydraulics you'll have money in a pump, motor, reservoir, control valve(s), cylinder, and lines. Depending on what you can scrounge will pay a large part in the end cost. I am not sure if you can have enough motor/flow at high pressure to help speed things up.
Taking careful sizing notes on an existing design is probably the best bet, followed by a chest of cash. IMHO it's not as easy as it seems at first.
-Matt