Yup, the port box would be the live-well. If equipped, there is a stern bottom hull pickup, sea cock, pump and supply hose that enters the livewell box near the top. In addition, there is an overflow fitting connected to a thru hull fitting on the port side above the waterline. It is quite difficult to retrofit since the existing tank liner does not come out and getting to the outsides of the tank and inside of the port hull to install fittings is a real bear.
By the way, the original tank uses a rubber plug in the base drain when you want to use it as a live-well. I supposed you could add some sort of aerator pump and just fill the tank manually with a bucket ( I assume you don't have the raw water wash-down option either)