Thanks for the comments guys.
To answer the questions - I have built up a nice workshop at home over the years, including a home made CNC vertical mill with which most of this car was made. There are only a couple of parts left which are original Mardave.
As for the flat floor, while in theory smooth would be better, it really won't make much of a difference I don't think. The reality is that the flow of air under this chassis will be heavily disrupted already at the centre chassis point by what's upstream - junction between alu bumper and carbon chassis, foam bumper lower edge and body shell. Plus there's that huge cavernous hole where the motor is at the back.
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