making a RPM reading using pin 8-14

i`m using arduino mega, with 3,2" tft, witch use pin 0 to 7, and pin 22 to 53
my free pins are 8 tm 14
i like to make two rpm readings, to show on my display

the problem is, I only can find examples like this witch uses pin 2 for reading rpm.
any help is appreciated,

The interrupt pins on the Mega are 2, 3, 18, 19, 20, 21.

However there is a more general interrupt mechanism - pin-change interrupts - read up about those
since they can detect any pins changing.