Running brushed universal motor at different frequency than designed
Brushed universal motors are largely independent of AC frequency, and as you have heard, will also run on DC. Their maximum speed is normally way above any synchronous speed referenced to line frequency. In their construction, the phase angle between the rotor and stator fields is set by geometry, not line phase. This is also why they run at high speeds - they just don't care about the line frequency. This is ideal for appliances such as vacuum cleaners and tools such as routers and planers, which don't need to maintain constant speed under varying loads. On the down side, they are typically not very efficient at low speeds, but for an application where they can run fast, that's not a problem.

As long as you get the voltage right, you'll be fine.

Variable speed controllers will also work well.