Hi JR: I'm yet to build my own version of these clamps. As they say, "Ambition killed the cat", in that case I'm bound to perish before my time is up.
The idea being, for one set of clamps to serve two purposes. Such as thin pieces or those that need to be machined in its entirety, top holding clamps would be an impediment to the job when its size, exceeds the capacity of a regular mill vise. For those cases, I feel that a solid and square parallel, bolted across the width of the mill's table on one end should do the trick, with an edge contact clamp, pushing the opposite side. I can see now that a tilted ramp would be necessary as an addition to a pivoting locking bolt. That way the front of the clamp would be moving forward and also exerting downward pressure of the work piece when tightening the locking bolt. Increasing the height of the clamp's body to accommodate the ramp, is not an issue since it would be in an open area. Your addition of micro roller bearings to the design, is an excellent way to facilitate sliding of the unit.
I'll be working on a design along those lines. Let me suggest to you, that the value of exchange of ideas can not be overestimated. You inspire me, I inspire somebody else and on, and on, and on.