I'm trying to run the Core of a K64 @120MHz but I don't see how to modify USBDIV to get the 48MHz it needs.
this is how I set it to 120 MHz:
FRDM-K64F at Maximum Speed of 120 MHz | MCU on Eclipse
And here is how I use it for USB:
USB CDC with the FRDM-K64F, finally! | MCU on Eclipse
I hope this helps,