There are two different gearing setups on the 960 Albion concrete mixer. When looking on the underside with the cab towards you, the pinion wheel is either on the left of centre or the right. This is determined by the squared off corner of the mounting bracket that faces aft with the pinion wheel being mounted on the same side of centre. The upshot of this is that the barrel rotates either clockwise or anticlockwise as the toy is pushed forward. At a rough observation about 10-15% of the toys have the pinion on the left with the right being normal.
I have just noticed the brace in the 'tool box' behind the cab on the left-hand model. This does not coincide with the left versus right pinion wheel - just later issues of 960.