I wouldn't want to give up swing power, you will use it more than you think backfilling dirt, moving the pile over, or to reposition the rear of your tractor while digging or stuck.
Shoot for full 180 swing, you will appreciate the space savings in your shed or fitting on a trailer. Your proposed swing geometry looks like it will be very non-linear near the extremes and may even lock. I can measure the pivots on mine if you don't have access to a good example locally. It uses trunnion cylinders.
How much hydraulic flow does your tractor have? I would use the tractor hydraulics and avoid the extra pump, tank, filter, relief, etc. My tractor is rated at 8.3 GPM and runs the 8' hoe fairly well between half and two thirds throttle.
For a backhoe or anything with it's own valve you can just cut the line that connects the loader valve power beyond port and the three point input. Run the power beyond to your backhoe inlet, and the backhoe return to the tractor's sump. The three point gets no supply when the backhoe is installed...in my case I have to remove the 3 point arms anyway while the BH is installed.
Depending how your system is configured it could be as simple as making a couple hoses and adding some quick disconnects. For ultra cheap, if the line is steel you can cut it and braze JIC fittings straight to the steel lines. We have done that on several backhoe installs where I used to work, usually when the tractor used metric or ORFS fittings (pretty much anything beyond SAE/ORB, JIC, or pipe) that we couldn't find locally and customer was in a rush.
Thanks for the info!. Yeah for the king pin I have designed bigger pin, 2" i think.
But How these "replacing spring bushings" work? If the DOM will be 2"OD 1.25" ID, and the pin 1.25", how they fit? I like that idea to go with harder pins and put replaceable sleeve bushings, but I do not know how.