Some information found in the internet, on the model;
It's interesting and instructing to try some simple calculations. The original 'Little Nellie' has a flight mass of 249 kg. Following the proportion law for volume (and mass, assuming the same global density) , the model mass should be 249 x 0,714^3 = 90 kg
The 'Little Nellie' was powered by a 72 hp = 45 kW two-stroke. Taking a proportionality exponent of 3,5 for the power, the model should have an engine of 45 x 0,714^3,5 = 13,84 kW, that is very close to the actual value.
My conclusion is that the model is disproportionately lighter. Its real mass is much lower than the flight mass of 90kg that could be 'right'...
Very cool. The presence of a horizontal tailplane in the model caught my eye. The original Little Nellie IIRC did not have a stab. I am not surprised as models need stick fixed stability as the RC servo control makes stick free operation impossible. The stab is critical for stick fixed pitch stability. The original has an offset gimbal which provided stick free stability that a competent pilot can exploit to mask the stick fixed instability.