[Robb]

They've put 4.6l modulars in FFRs, but they are supposedly very difficult to fit. (need lots of custom work).
5.4 is same block, so I'd say it could probably fit.
Problem is engine width, not height.

Look around on the web, there is at least one build site for a 4.6 cobra. He should have lots of info for you, that will apply to a 5.4.

-Robb