We've got quite a few guys running them down here. We have a ready source of the quad cam 5.4 from our locally built Ford Falcon.
With our strict emissions laws it's now pretty much a choice between the 5.4 and the GM LS series engines. Due to it's gigantic proportions and mediocre performace the 5.4 seems to be the least popular option.
To give you an idea on difference in dimensions:
The 5.4 is even wider because of it's taller deck height over the 4.6. The only way these modular motors seem to be making any decent power is with forced induction.
I think their achilies heel is the bore spacing. Ford designed the motor with a really tight bore spacing to keep the motor length as short as possible for Front Wheel Drive applications. This put a cap on the max capacity of the motor such that to get to 5.4L they had to increase the stroke so much that the motor is undersquare (stroke longer than the bore size). It's a shame because they have these fantastic 4 Valve heads that have huge flow potential but a bottom end that won't do the revs to support them. I guess this is why the factory went for forced induction to increase displacement.
Cheers