Yeah, they wrote: "Boeing will conduct a PROTOTYPE flight
demonstration in the first quarter of 2008, using a modified 480-
gallon centerline fuel tank to house the IRST system."

So I assume they use the bigger, F/A-18E/F tank for tests (not a 330-
gallon tank used on F/A-18A...D - sorry, but I neither have any idea
about the 350-gallon one, nor it is mentioned in the text).

But also - later on: "The PRODUCTION system will contain more than 330
gallons of fuel in addition to providing the IRST capability."

That makes me think the idea is a bit similar to ARS ("buddy refueling
store"), with a device placed inside a tank, and empty space filled
with fuel cells.