That was me…and that’s how it’s done for the Sportsters… You’ll pick up a set of B6/B7 bases, then a set of universal sliders. Here’s an example of a seat base by Wedge:
http://www.vividracing.com/catalog/wm.php/images/WedgeEngineering.jpg
The seat belts will mount to the base itself. Then on top of the base, you’ll use a universal slider set (It think by wedge as well:
http://www.turnermotorsport.com/image/interior/seats_Recaro_sliders_with_tabs_top.jpg
Then the seats mount to the sliders. As a note, the sliders have 3 holes for height adjustment. In this application, if you want to use the lowest height, you’ll need to cut off the two lower mounting points/holes otherwise they’ll rub along the carpet…again, they’re “universal”.
Different seat brands/designs may need a different set of bases/sliders…Sparco, for example, makes their own base:
http://cdn3.volusion.com/frvnx.fatkq/v/vspfiles/photos/SPARCO-MOUNT-5.jpg
Hope this helps clear it up a bit.