When I was in the USAF as a ground support equipment technician, I worked on a lot of motor generators that are single shaft 60Hz motors to 400 Hz generators. Many of these motor generators were older than I was at the time. Some of these were called the MD-1 or -2 or -4. They ranged in size from 15 KW to 75 KW. When I was stationed At RAAF Lakenheath in the U.K. we changed over to 50Hz to 400HZ equipment from the older 50 to 60 Hz then 60 to 400HZ units. One piece instead of two is easier to maintain and works better.
400HZ power is standard on aircraft almost every where in the free world. some of the reasons are above.
