I found it easier with the battery and tray out to be able to route the snorkel. The airbox just pulls out completely. If you have the SVT MAF to go with the airbox and snorkel, it would be better to use it. There is a definite increase in airflow between the stock and the SVT intakes.
Zetec Crew #137 / Boosted Crew #88
2003 Liquid Grey ZX5 SES - see profile for pics