i believe some boats came with a shaefer 4:1 mainsheet using this block at the top.
http://www.sailpix.com/email/olson30/2010/4600.html
http://www.sailpix.com/email/olson30/2010/4601.html
we currently have a 3:1 6:1 using the original fiddle at the top and a double fiddle w/cleats at the bottom. like the image below but instead of the double block at top we have the fiddle.
http://www.mauriprosailing.com/Harken/images/pi/HAR332.jpg
our setup slightly cobbled together but not bad. if we had another one of these shaefer fiddles we could split them apart then put them back together making the top fiddle a double and increase the purchase to 4:1 8:1. it would be a bit cleaner too.