Fe's are great engines, but hard to swap in.. The best thing is to wake up the 400 with a cam intake carb & exhaust. There is a BOATLOAD of torque hideing in that motor. http://home.earthlink.net/~bubbaf250/index.html
If Real POWER is what you crave....the (385 series,429-460) motor is a BOLT IN. http://429mustangcougarinfo.50megs.com/