Whoa there pardner
before you go putting time and effort into rebuilding this boat, you might want to consider why it was disassembled in the first place.
Most likely the boat has other significant issues or is unsafe in some way
Does it have front and rear support Pillars? Is it broken or cracked anywhere? Its between 12-15 years old. You can proabaly get an intact "lose control" for $100.
It is unlikely that another brand's seat will fit in the boat. Just because it was a "good Deal" doesn't mean its worth the effort to get into a river worthy state.
Even more importantly, using this boat to learn in is a handicap. You will find the sport harder, more frustrating and less comfortable, than in any number of more modern boats, that can be picked up cheaply.