One minor correction that I want to add into the discussion is that the Kadee couplers for S scale are #802 and #808. The only difference between the two is the 802 is cast in black plastic while the 808 is cast in brown. The 805 is the older style all-metal O scale coupler.
I also wanted to add that there are a few sites on the net that can help you answer your questions on S scale.
www.nasg.org (National Association Of S Gaugers)
www.sscale.org (S scale Special Interest Group, NMRA)
http://trainweb.org/crocon/sscale.html (Craig O'Connell's S scale website)
www.sscalenews.com (S scale site with some tips and older catalogs)
Hope this helps,
Robyn (CarolinaRail)