Flux has single speed and if you switch to CD you will have also have to change the motor as transmission has 2.2 ration and CD has 1. You can compensate something with bigger
spur and pinion.
Standard Flux transmission with 44/20 equals CD with aprox. 49/10, but with pinion that
small you are very limited with motor diameters.
There is already finished project, not only drawings. With 3 differend battery positions. Inside TVP's or in batterybox with two mounting options.
On first picture is kit wit 3mm tvp's, on second with 5mm.
Dejan