You may not realize that all the "boxes" on the boatersland page are actually menus...click on each one to see more options. You'll only want the angled back if your toilet will lie against the hull...there are two straight back choices--choose the shorter "standard" height if your toilet will sit on a raised platform...the "tall" one if it will sit on the head sole. There are 3 flush options: single button, 3 option, and the 4 option Smart Flush panel.
Fwiw, Boatersland is my favorite Marine Elegance retailer.
----Peggie