Hi Energumen
The 'dozer looks like a Fowler as you suggested, and the Scammell used a 10.3litre Meadows which had started out as a diesel but was converted to petrol in a Scammell/Meadows collaberation.
Following on from the level crossing incident, one of the agency drivers I worked with was with the RE somewhere in Germany and his pal, driving a similar outfit to the one pictured, decided he could beat a train to an unmanned crossing. Unfortunately his speed/distance calculations were somewhat out and the steam loco ploughed into the side of the Scammell, removing the front axle but without de-railng the train.