2.1-3. The vehicle's original, manufacturer-stated curb weight may not exceed 4200 pounds.
3.1.1"Minimum tubing size for cars weighing under 3000 pounds as raced"
The judges look at eligibility of the car/class-of car based on curb weight.
The Tech inspectors look at the vehicle based on actual weight - based initially on typical comparable Race-weight from SCCA or similar rules books. You will find that those rules give weights that are difficult for club racers with safety equipment to get down to, so most inspectors err on the side of your car being heavier.
3100# is more than #3000, and yeah, as raced means Wet with driver.
In planning, pile everything in the car, all materials going in on or around the car that make up the car and theme. Add rolls of duct-tape, 2 gallons of water, fuel in cans, oil in kegs and your heaviest driver. Add 1.3x the estimated tube for cage stuff. Add a case of beer (driver water/breakfast weight). Weigh.
If you get below #3k and get a scale cert (like from a cert'd truck scale) with a pic and inventory list of everything in the car as weighed - they can bitch, but the rule is #3k. --Unfortunately if there is a fuss you will lose because a good inspector can always find a legit reason for fail - usually around a perforated or incomplete weld.
Light is good - Good luck!