ON the MG and USH ones I have seen, the outrigger beams slide out and in from the boxes on the side of the frame. They also have the crank locations as mentioned.
Another option, I have seen catalogued is Locomotive Workshop, the business that Jan Lorenzen ran for some years. They advertized a kit for a 250 ton crane. Their kits were craftsman style, and were brass mostly. I have never seen one in person.