Unused pins/functions of Arduino Mega (ATmega2560)

I apologize if this topic has already been discussed, but ... I couldn't find it anywhere.

I am talking about the Arduino Mega board. I need to use the inputs to the other 16-bit Timers/Counters, namely T1, T3, T4 (T5 is the only one connected to a Digital Pin).

I can of course wire the pins from the CPU to a board, but I need to know if anybody ever released a pins_arduino.h already modified to include the relevant definitions.

Or if somebody can help me in defining them.

The signals/functions involved are: - pin 8 / PE6 / T3 - pin 27 / PH7 / T4 - pin 49 / PD6 / T1

T5 (PL2) is already connected to Digital Pin 47.

Thanks in advance!