This is pretty crazy.. saw a link to it on Stangnet. This machine shop is producing cylinder heads that are 4-valve/cylinder for Ford 5.0 pushrod engines. "Bolt-on"... I'm sure it's more involved than that but it's still interesting.. they have a valve bridge that actuates 2 valves at once from the 1 camlobe and pushrod that you have coming up from the bottom of the engine.
http://www.araoengineering.com/Ford/frdsmb.htm