[pnaleahy]

Indeed Derek Hughes devised a system of fitting the J Type electric overdrive to the Bristol motor and gearbox and supplied all parts required. The system relied on removing the existing gearbox extension which contained the original sliding mechanism to the tail shaft, replacing the extension with a transitioning casting and the J Type overdrive unit and replacing the tail shaft with one with a sliding yoke.
The lubricating oil recommended by Derek Hughes for the J Type Overdrive unit was Castrol Transmax F automatic transmission fluid.

I have one of these units fitted to my Bristol 400 and a Bristol 403. They both work flawlessly with the recommended lubrication to the correct level.