The PRNC which is the 4 day course involves another 2.4km run, 2 swim tests and a 4km run.
The 2.4km run you do a bit of cardio beforehand, so I'd recommend before practicing road running, do about 10 mins of warming up including shuttle runs and the like because when you come to the 2.4km test your already knackered!
After the 2.4km you do a military drill type session in the gym, learning how the PTs will put you through your phys assessments. This is just push ups, burpees and military style situps. All easy stuff but just be prepared to push yourself.
The 4km squad run is more then a run...I'll leave that for you to find out about haha!