Timer1 can work with some pretty quick external input clocks. Check the electrical specs
section TIMER0 AND TIMER1 EXTERNAL CLOCK REQUIREMENTS.

Look at the specs for T1CKI High Time, T1CKI Low Time, and T1CKI Input Period.

With a pickup coil tuned to the frequency you're measuring, and the /64 output, it should
be pretty simple to measure your freq range.