Following on from the successful testing of the pioneer 364A 4-6-2 of 1966, Chief Engineer Jochann Ketterik decided to apply the Doherty six-cylinder compound drive to a goods locomotive. Not all design features of the 364A were retained in the 564A, however. The most obvious departure was in the mounting of a wide firebox above the rear driving wheels. This was done to minimise the overall length, although the RSR had large enough turntables at all its major MPDs. Also, the 564A had bar frames. The steam-jacketed cylinders and intermediate resuperheat of the 364A were retained. The use of a Vanderbilt tender indicates that there was no desire to run the engine tender-first, although a semi-rigid tender drawbar was fitted. Other standard features included a mechanical stoker, roller bearings on all axle and running gear journals and vestibule cab.

On trial, the 564A very quickly showed both its good and bad sides. The engine was very sure-footed, accelerated well and rode very smoothly. The exhaust system provided more than adequate draught and the running gear showed only very low wear and tear. The biggest problem was caused by the location of the firebox. At the start of a run, steaming was excellent but soon suffered drastically as the sides of the grate became clogged with ash, which would not shake down properly, owing to the very shallow slope of the ashpan. The irony of this situation was not lost on crews who remembered the original 344D 4-6-4s. Additional ash hoppers outside the driving wheels (not shown in the drawing above) relieved the problem but caused another by allowing ash particles to sift down onto the crankpins.