I think you would be better off with the Cadet 3 if you are going with American Standard.,
Performance is similar between the two, they both have 3" flush valves, even if A/S says the Champion has a 4",
It necks down to the original 3" dimension.
It's a funnel.
The Cadet 3 is an easier install and takes up less space in the bathroom.
Just make sure you open the boxes and inspect carefully before bringing them home, save yourself a trip.