Just a correction. WDP2 was also a 3100HP locomotive only.
Only WDM2 was a 2600HP loco that was upgraded to 3100HP. The upgraded 3100HP engine was used to build WDG2 and WDP2 locos. When the new diesel loco naming convention was adopted, WDG2 and WDP2 locos were just renamed to WDG3A and WDP3A. It was just a renaming and not a conversion.