UPDATE: the CNC router slides didn't last long with the weight of this hammer and the little roller bearing units in them fell to bits, I have replaced them with a simple steel block with a groove milled in it 6mmx6mmx200mm and 2 grease points per side.
The hammer is 69kg the anvil is approx 740kg and is a horizontal stack style which is not ideal as a stack anvil is preferably vertical segments but it seems to work quite well, working surfaces are railway line, the ram is 2.5x10inch.The foot operation actuates a 2 position 5 way valve via i linkage with a spring return to keep everything up the top and the hoses as low capacity as possible, the ram ports also have quick exhaust valves fitted. It has toyota 4runner bump stops which protect the ram from topping out, they are either side of the ram to avoid unnecessary side loading of the slide. The hammer rides on CNC router slides, an idea from BIG DOG FORGE which he used on his excellent mechanical power hammer, here is his video on it • Blacksmithing Power Ha...
As with most of these DIY power hammers mine is built mostly from from scrap, which is why they all look so different, so scrounge around in your scrap pile and get creative.