According to information from reliable sources, it was originally intended to rebuild 100 class 34-600 and 34-800 locos as class 39, as well as the class 37. Although the project was a great success technically, apparently the costs incurred were somewhat higher than anticipated. Accordingly, after completing five, it was decided to end the series at this point.
The second series, the class 39-200, is being assembled from imported components, and will in effect comprise completely new locomotives. Transnet Rail Engineering and EMD are collaborating on this project.