Yes you can, however you will need to utilise the existing airbox. There are many makes of OTR for the 5ltr 304, the most well known being SS Inductions, and Aunger. I'd recommend the Aunger Cold Air Intake which is what I use myself, and have found it makes a a noticible difference although don't expect huge gains.
The MACE Cold Air Intake also looks really good, and has a lot of great reviews. It's not an OTR but I hear it works a treat. Checkout their section on the forum.