The Glenwall Vormax wallhung by American Standard is a gravity flush with their Vormax technology. Two flappers in the tank to distribute water to the bowl. It's a taller comfort height bowl, about 1.5" higher than their pressure assist Glenwall.
Just a few parts to keep track of.
Two flush valves with gaskets.
And it might be a good idea to pick up some retrofit bolt caps in case the threaded bolts are too short for installation with the standard bolt caps.