If you are going to use coil overs on the Fairlane the upper shock mounting point is not strong enough to hold the vehicle weight. You will have to make a mount to hold the upper end of the coil overs.
I would look into the Wonder Bar rear end that Fatman is offering for the Mustangs (same as yours). See the upper coil over mount he is using and go from there.
Actually that Fatman suspension would be very good in the Fairlane. We were using it back in the middle 60s with quarter elipticals.