That's a 19' boat.
My experience with "free boats" is that they need work a lot of the time. Like transoms and/or floors. Nice part about these, is that you don't have to worry about the stringers (all alum.), or any glass work, so they make nice DIY projects. Hull has all welded seams, so those won't be an issue.
The guy is dreaming if he thinks the motor is worth 3500, but that package may be worth what he's asking for it depending on how it checks out. My 19' came with a 70 on it and it's much stronger than one might imagine a 70 would be on a 19' boat. 8' wide shallow vee that doesn't weigh much is very easy to get on plane, and it will stay on plane down to just silly speeds. These boats are wide, so they are stable. They ride pretty rough in chop over about 18". Until then, they do a nice job of keeping everyone dry. Great ski, fish, cruise combo.
Rivets may be very difficult to get to, requiring that the floor be removed.
Best case is that his "leaking rivets" is actually a plumbing leak in the lines to/from the live well (every one of these I've seen has one). No fun to deal with, but much easier than removing the floor.
Another thought, if the boat is gong to be trailered, who cares if it's leaking a little? Just pull the plug when you're done using it for the day. If it's going to be left tied up to a dock, that's something else all together.
I would plan on getting dirty during your purchase inspection and crawl around under the boat from front to rear looking for anything obvious. While under there, look the trailer frame over. It's getting older, so potential for rusting through is there.
Bottom line, where we are in Florida, we have the ability to travel quite a distance on both fresh and salt water. We sold a pretty nice pontoon boat as it was taking us FOREVER to get anywhere. Deck boat allows us to cover some serious ground when we want to. They are MUCH quicker than a 'toon!