5.4

It does fit but it is tight. You still need everyting you need to install a 4.6 i.e. tubular k-member, hydraboost brakes, etc, plus one big cowl hood to fit it under.
 
Hey man, if you can afford a lightning motor....do it. I had a lightning before i bought my house and with a built motor and a kenne bell, you can make gobs of torque with it. Mine made 635rwhp and 765rwtq, i always wondered what it would be like to have it in a mustang...ridiculous!

Anthony