design, Would increasing the size of the hydraulic cylinder increase the load capacity or would you also have to change the hydraulic pump (big money) in order to pressurize the larger cylinder correctly plus frame, weight of machine, design specifications of pins and fittings HMM! sounds like maybe a bigger tractor should be on your wish list rather then overstressing your current machine sell it before it gets bent out of square by tweaking the loader frame and mounts and put the money towards a bigger tractor if you go big enough it may even be less expensive then the one you've got if you pick up a good used one, though if you have implements they'd be to small possibly. Maybe a package deal swap with a retiring farmer who's looking to downsize.
Steve