Yes, to both Ken and Moss's points, but here was my thinking:
1. By mounting the QA plate vertically on the land plane, and using the shortest hole on my toplink, I think the tendency for the tractor to climb up onto the attachment will be much less - how much is yet TBD. IMO, the normally angled QA plate forces the lift arms up when pushing hard. To use a landplane or box blade effectively they must be able to float.
2. My limited experience with this old 3-pin setup and it's push bar so far shows that the push bar makes a big difference. I can push my finish mower or rough-cut uphill or into areas, using float, where I would've had to lift my QA attachments slightly to continue. Having the ability to transmit force down low, parallel to the ground makes a significant difference. This 3rd point is down below the center of the wheels, similar to the fixed drawbar on a 3pt tractor in comparison to the drawbar on the 3pt lift arms. The force when pushing tends to push the tractor down slightly rather than lifting it, though most is transmitted parallel to the ground. Both my 3-pin mowers simply hang underneath the lift arms, with no toplink used, and all pushing is done with that push bar...
Whether or not I can effectively push the 500 lb land plane (485 + the QA plate), especially in float, is yet to be seen. But this EA one at least should let me experiment to see. Meanwhile, I can pull it, as intended...
Also, this discussion has been quite valuable - for example I've now concluded that for a hydraulic, adjustable toplink to work effectively, I can't simply "tee into" the existing curl circuit and let both cylinders move at the same time. That second cylinder would need to be independently controlled by a valve (whether mechanical or electric solenoid) -- otherwise you could end up with undesirable placements - such as the toplink fully extended and the lift/curl cylinder retracted.
This brain-storming is invaluable!
