In the olden days, an avionics workshop would indeed have a motor-generator, with the motor being 110V 60Hz or 240V 50Hz, or whatever the local mains was (or even a diesl engine), and the output being 115V 400Hz 3-phase, and where you 'borrowed' the 26V 400Hz via a transformer.
Curses.... in those days they were just sockets on my workbench, and I didn't even ask where it came from.
Now I'm looking at trying to help out people who no longer have access to an avionics workshop, but who are still looking for 400 Hz supplies without paying a fortune...
I'm still hoping somebody has addresses for surplus equipment, or valid circuit diagrams.
As I mentioned, I don't think aircraft equipment will appreciate the near-square-wave output from the simplest of DC/AC converter circuits. Saw-tooth or distorted sine wave will do, I think, considering the mostly inductive loads.
Thanks for helping already!
CJ