You sure can use your 9C on 72Mhz, at least at fields that still allow it, some do not due to new fields that are too close for safe operation on 72Mhz, also, major events are pretty much 2.4Ghz only, sine no one wants to run transmitter impounds at large events.
Your 9C can also be used for 2.4Ghz operation with a conversion module, such as this one.
FrSky DFT -Futaba Transmitter Telemetry Module
The FrSky receivers that work with that module are also very reasonably priced.
Futaba used to make conversion modules, but apparently they dropped them, and Spektrum used to make a module for Futaba radios, but they too seemed to have dropped them.
There are Spektrum compatible modules from Hobby King, that bind to Spektrum receivers, so that's an option as well.
Good luck and welcome back!!
Pete