I am having a hard time finding the correct device header for a P89LV51RC2 device.
I found REG51F.h, but I am not sure if it is correct.
What header should I be using for the device above?
Go to the Device Database entry for that device - it will tell you: http://www.keil.com/dd
Note that there is nothing magic or special about these headers; they are just perfectly normal 'C' header files - so there is nothing to stop you writing your own...