It's not a true 4-3 like you'd see the Bison, New York Giants or Dallas Cowboys play. It's a 4-3 under with a lot of the same principles as a 3-4 defense. It's just a one gap scheme as opposed to a two gap scheme. Here's a piece from Field Gulls showing Seattle's front during the last season Gus was there as a defensive coordinator and previewing Dan Quinn's ascendence.
http://www.fieldgulls.com/football-b...inds-of-change
Emanuel will likely play on the edge in this defense in some capacity.