I was curious how the mini transferred power to the wide gauge unit, found this:
For many years there were no true broad gauge locomotives. Initially horses were used, but from 1888 broad gauge hauling and shunting was undertaken by narrow gauge locomotives mounted on unique vehicles called "haulage wagons". These were another product of the many-sided genius of Mr Geoghegan. The way in which the haulage wagons functioned was most interesting. A narrow gauge locomotive was lifted by an hydraulic hoist which stood astride a short section of gauntletted, dual gauge track. A haulage wagon was then propelled under the narrow gauge engine and the latter lowered between the frames of the former. Both ends of the locomotive were engaged in the wagon and the wheels of the narrow gauge engine rested on rollers whose shafts were geared to the running wheels of the haulage wagon at 3 to 1 reduction. Thus, temporarily, a narrow gauge engine became a broad gauge geared locomotive. Until the advent of conventional broad gauge locomotives, this was the exclusive form of broad gauge motive power. They were permitted to work loads of as many as thirteen broad gauge wagons fully laden. Two out of the original total of four of these haulage wagons, with the two 1921 steam locomotives in harness, were working in September 1964.
Found it very interesting.