As I had nothing else to do, I looked. There is not all that much to change, IF, IF, IF, you have a complete gen set. Looking for individual components for the control cube would be a PITA.
1. Main gen. Figure 19, Item 15.
Filter Assy. Figure 14, Item 22.
Filter Assy. Figure 14, Item 6.
Control Cube, (complete Assy.) Figure 6, Item 6.
Load Output Door. Figure 5, Item 112.
There are a number of components to be changed in the control cube, and I didn't count them, as it make more sense to change the whole cube, then try and find the individual parts. But its possible.
How the output load door could be different, I have no idea, and there was no info on what door was for the 400 hertz model. Sounds fishy to me. Probably a non problem.
Still, I am sure it might be not as easy as one might think. Still, might be fun!