Per the spec sheet, there is normally 3/4" behind the Vespin, when installed on the 'exact' rough-in, so yes, it should fit. You can fudge the placement of the adapter a little, too, so you should have no problems. The only issue might be the placement of the water supply shutoff, as the skirt is wider than a 'conventional' unskirted toilet. I have a Vespin and a Carlyle in my home...both work well. You might consider the Vespin II, which uses less water and has a few other enhancements.