I did not say that would be a weekend project, now did I? :sidelaugh:
Bart has made some good points but I don't know if they are deal breakers or not. John hasn't revealed why he wants to add power steering. Perhaps this is for a FEL project and that would make sense. Ideally, a slightly larger pump would come in handy but there is no pressing need to go that route for the moment. Yes, the ground speed will suffer somewhat and so will any hydraulic motorized attachments that are connected to the PTO. But for FEL work, none of that matters. The existing pump will still deliver the same pressure it always did and that's what pushes the tractor into a pile of dirt that needs to be picked up.
It has been done by "others" in the past even though clearance is tight. Get everything you can from the Deere. Steering wheel, steering pump, steering cylinder, all brackets and hoses. John will have to remove his engine, battery, oil tank etc but should keep the pump in place for the moment. The existing steering wheel, shaft, gear and drag link must be removed and then the fun can begin.