Are there any lengths of exhaust pipes that are 55 to 75 inches long?

If so, put a resonator in the middle.

If for some reason you can't use a resonator
it is also possible to kill a drone noise with a T-stub,
which is a dead end length of pipe off a T junction

Someone in the family
or your group of friends
good at math?

Have them read:

http://www.audioholics.com/education/acoustics-principles/helmholtz-resonant-absorber

if you look at the intake of the new Ford 6.2 V8 you will see T-stubs in use