The reason the Cavalier igniter was used was because it packages so much nicer and cleaner than just custom mounting them somewhere. It's pretty simple, you just tear the guts out of the cavalier igniter and wire it like the pictures show a few posts up. Also, the 4 post igniters were used. they were used to in conjunction with the double coils and cavalier igniter. The cavalier igniter just served as a rack to mount the coils.
+1 To zoro on the explanation for the relay powering the coils.