Got the info, posting it since someone might need it later.
The doortag with max axle loads doesn't appear before 1973, so this data is from a similar Challenger, same engine, a 340. It will be a newer year model, don't know if it's a 1973 or 1974, but it makes no practial difference since the cars are the same for all practical purposes.
1050 kg, 2315 lbs front axle.
1100 kg, 2425 lbs rear axle.
The max payloads vary from car to car, depending on equipment, but as
stated, these datas are from a car like mine, with a 340 V8.