It's been 10 years now since my 4/4 Sport went but I do remember the Focus Haynes manual covered the engine which I passed on to a TM member a while back.
I recall the air box being angular this vid maybe helpful and also reveals the number WA6535. This link gives you the dimensions as a check.

[video:youtube]
[/video]

2009 4/4 Sport Henrietta
1999 Indigo Blue +8
2009 4/4 Sport Green prev
1993 Con Green +8 prev