Are you asking about just the engine or the whole car?
You can swap the engine over with just bolt in parts (i.e. mounts) no problem. I'm not sure if the k-member would have to get changed.
You'd need a matching transmission and all that hardware. The hard part would be you would need all the electronics to run the engine. The PCM and all the harnesses, or a standalone for it.
Exhaust would have to be fabricated to fit (though not that different from GT exhaust).
You'd really want a new 8.8 axle. Your 7.5 wouldn't last long behind it.
New front springs wouldn't be a bad idea, but aren't a 100% must.
The fuel system is a bit more complicated. If the engine is set up for a return style system, you'd need to switch out the rails to a returnless, or set up your car for return. Your pick, really, and make sure that your PCM and wiring matches whatever route you go (or is tuned for it.)
If nothing else, depending on your location I have a fox roller and a whole bunch of modular parts that would be just the perfect home for a 5.4 4V.