The plan

I don't intend on dismantling the Roadster and then starting the conversion. Instead, as Smarts have a subframe with the rear suspension, gearbox and engine all mounted on it which is then bolted up under the car it makes sense to buy a set of subframe parts and build a fully working electric drive version, once it's all finished and running this can then be easily swapped with the petrol version so it should then only require minimal effort to finish it.
I'll be using a full AC motor system as they have a wider rev range, regenerative braking and are more efficient than a simple DC motor. The cost will be higher but the effort will be more or less the same so it would seem to be the better option.
Normally you wouldn't need a gearbox with an AC electric motor, they have a wide torque range and are high revving but the one I plan on using with a controller with a 80v limit means I'll probably need to be able to change gear ratios so that I have some acceleration at lower speed and it won't rev out at the top end.