which engine for Factory Five

[MKS427]

I have a 351W based 427 570hp and it is fun. The Coyote is a great engine, in fact I heard the the person that won slalom course last year was in a Cobra with a Coyote. The FEs will set you back at least 50% more and will not make as much power per cu in, but they are the right stuff.

The other things you might consider are:

The complete kit, it has a significantly better suspension. Coil overs, 3-link rear or new Mustang IRS, tubular control arms, and a rack engineered for the car.
Hydraulic clutch.
EFI, in which case you will need a double collector in the header with a bung for the O2 sensor. FFR has these for the Coyote.
Factory Five headers are not good with raised port heads for the Windsor. GP Headers makes them.
If you get the Wilwood pedal kit, you should verify clearance for travel on the clutch pedal. You may have to do some grinding on the frame work to get full travel. You will have an easier time if you do this before anything else.
A proper shroud and better fan(higher amperage/>0.7" @ high flow) for the radiator.
Not locating the battery where FFR put the reinforcement. It is in the center of the largest space in the trunk. Move it all the way to the right of the trunk, or Breeze sells a kit to put it in front of the engine.