I also have the Speeco QH. I have adapted each of my implements to the Quick hitch. It is not too much work usually, to adapt each one. Sometimes you have to drill a new top hole, usually have to cut a pc of bushing, etc. The one implement that was tough was the Tiller, 'cause there were frame geometry roadblocks. It works now, but required some eccentric bushings, welded to the lower pins.
One nice advantage to using the quick hitch, instead of any of the quick setups that do not tie the arms together: You never have to screw around with the turnbuckles that hold the arms from side-sway. Once set with the arms attached into the quick hitch frame, and turnbuckles tightened and pinned, you simply hook stuff up.
When I look at the pics in this thread showing the Harbor Fright QH, I can see it is IDENTICAL to the Speeco product.
I modified my Speeco several times. After the best height for the top hook was determined by a quick survey of my then-existing attachments, I cut off all the "extra" height of that holed bracket that is welded to the top of the QH frame. Otherwise, it interfered with my hydraulic hoses. Also, just lately I added a new channel, of 2x3 angle iron, to the inside surface, each side, to form a new pocket for the tractor arms to connect to. Of course I drilled the hole clear thru the new steel part too, and use longer pins. Doing this gave me 1.5 inches more clearance between each 3-pt lower arm and the inside of the tire. I still need to get some pics of this for you guys.