Man I knew this guy who shoe horned a 460 in his 88 mustang, it was a tight fit no doubt, but man that car was incredably fast for a bone stock 460, it was all torque.
He ended up selling it after he melted about three sets of tires in 2 months....lol
I know them 4.6's can be built to be pretty bad - there are plenty of off the shelf performance parts to be had, plus like you said they are alot lighter then the old cast iron V8's
Goodluck on your swap, post some pics as you progress.
Late Cp