Should be fine with a 7.2. My Deans Fire Boat also has a 480 motor and goes far faster than scale speed with 7.2v., planes about half out of the water.
I am in the process of converting to brushless using a 1050 kv 140 watt turnigy motor. More on this when I get the speed controller in and the lake thaws.
Regards
Tom

HI there. I have bought your kit off Paul on Ebay. it is my first RC build.
It came with a JP 480 motor rated to 9.6v. it ok to take it to 9.6 or safer to step down to 8.4v or 7.2v?
John