In the wording of your original question, are you looking for something with 450 lbs payload, or something with 80 lbs over 450 lbs payload?

Are you looking to run full fuel with the passenger, or are you willing to consider running it at reduced fuel load when "taking someone for a ride"? As you look into this more (at designs with 450-550 lbs payload), you will see that based on the fuel tank size, these most often can be run in the following combinations:
Pilot + full fuel.
Pilot + small child + full fuel.
2 200-pounders + way less than full fuel.

Just saying, think about the mission. In a low-and-slow flyer like that, the mission isn't going to be 2 people + full fuel + bags, etc. Local 1/2 hour to 1 hour sightseeing flight, will only need ~8 gallons and that will still include the required day VFR reserve.

If you really need more payload, then you will need to look at bigger airplanes. You will find to go from 450-550 lbs payload to 600+ lbs payload is a LOT more money.

Beware of manufacturer payload claims. Try to find real numbers from customer-built examples if possible. What looks like a 550 lbs payload airplane in the brochure may really end up at 500 lbs or less in the "real world". Sure, there's lots of things you can do - I used to say lightening up the panel would be one, but that's one area where great progress has been made over the past several years. There's other areas - smaller wheels/tires/brakes, no autopilot, smaller fuel tank, no lights, no paint (metal airplane)...