seagull nemesis nxt are allowed.
If this is a Formula One class (Goodyear, 190 CI, later 200 CI) only class, then the Nemesis NXT would not be legal, since it was in the Sport Class at Reno with turbo charged IO-540 or IO-570 engines pushing close to 400 mph. The earlier Nemesis would be legal, but they are two very different aircraft.
If this is a strictly scale event of F1 designs, you will be at a huge disadvantage with a Rivets compared to the newer high aspect designs. The difference in induced drag in the high G turns of the older designs is the difference between winning and losing. If they allow you to fudge the wing span to a similar span as the Nemesis or Sundowner, then you have a chance. For instance of the 200 plus designs that have competed in full size F1, about 25% have been close variations of the Cassutt. In recent years a popular modification has been the so called "Wilson wing" which decreases the chord at the root and tapers the wing, thus increasing the span.