@kats glad you are excited. The computations are based on the figures you supplied from the Datsun Japanese aero study and the windtunnel tests done in the USA. The formula used to calculate it is based on published figures, Datsun quoted 150ps for the power, I used their figure. All the data is readily available, no hocus pocus. If you can provide the aero figures for the European 240Z I would be happy to calculate the result.
The aero horsepower required to push the standard 240Z through the air to achieve 125 mph would be around 140bhp, this doesn't take into account parasitic drag losses due to tire friction etc.