The photo that Michael refers to is the following:
The above supposedly is a replica of the following:
However, the above depicted car is not the twin-engined prototype, it is just a streamlined T13, probably 8-valve; according to Steinhauser, (yes, I received the "little book" yesterday) the only such prototype is the one depicted below:
It can be easily seen that this is a totally different car. According to Steinhauser, the car worked well, until the gearbox (which was the regular one for a single-engined car) collapsed. The gearbox obviously was not build to cope with the high torque and power.
Conclusion; the twin engined "Bugatti" beside the airplane is fantasy, a nice fantasy, but still. I wonder what gearbox was used....