Thanks for the helpful suggestions. I'll double check with the tractor dealer's service guy about twcoffey's concern about limiting pump life, as well as firefarm's comment about valveing and if continuous flow is available. I've sent a PM to poleframer asking about his experiences.
I don't know the actual piston diameter, but the outside diameter of the cylinder is a bit over 7 inches. Assuming the piston is 6.5 inches in diameter, and limiting max pressure to 2500 psi (tractor max is 2850 psi), that should give me a 75,000 pound push (area x pressure). I would then size the fame for 100,000 pound design load and a 1.5 safety factor. Using A36 steel yield of 30,000psi would require less than 5 square inches of frame work to resist the tensile load. I expect the bending load for the top and bottom members of an H-frame press would the critical design factor. I am thinking that 12.0 inches inside to inside dimension of the frame would be the minimum width. A C-frame press would be a bit more complex, but might be worth the added working room.
Any and all comments on the above thinking are most welcome…