another way to approach this
In order for anything to float, it has to displace its weight in water. Therefore, if you weigh 320 lbs, and the boat and gear adds another 50 lbs, you need a boat to displace at least 370 lbs of water. Water weighs about 8.33 lbs per gallon, so the boat will have to displace 44 gallons. That means 44 gallons will have to be below the water line. Ideally, you probably want as much boat above water as below, so you'd be looking at a 88 gallon boat. This probably puts you well into the creek boat range:
Pyranha H3 255 (or M3 or G??), Prijon Embudo, Wavesport Y, etc.
Hope this helps.