[Scuderia_Turini]

Hello Ian,
Offset gears and motor mounts are definitely for ultimate performance scenarios. I think that in practice one would fit a motor pod, pinion and crown gear from the same manufacturer. However, as you say, the pinion is less crucial. 

Some people will adjust the rear axle bearing supports so that the axle moves upwards and achieve the relative lowering of the motor and chassis that way. Doing that would mean some precision engineering or a bit of a guesstimate to select the crown gear. 

Leo