Each motherboard will have varying amount/location of USB ports, etc., on the rear, but, MB normally comes with a new back plate/IO shield that matches the numbers/location of ports....
As long as the IO shield on your case is removable, no issue...
Food for thought....how isZ270 really an upgrade over B250, if not overclocking? Performance will be identical, so, unless you need the extra USB 3.0 header from a Z270 board, I'd think this $100-$140 purchase over a little more carefully, lest you be disappointed with identical gaming performance...