I have a 2004 BA XL V8 ute with 4speed auto and yesterday it did the engine.

So been looking into trying to get another engine for it and I was wondering if the XR8 motor (5.4 4valve) will just bolt right onto the auto and plug up and start or is there a whole lot more changes required?

Also is converting to the XR8 motor worth it?

Any help and advise would be great.

Harness is different but could be modified to fit the engine. No VCT wiring required on 4V engine of course. A 4V PCM and harness would speed things up.
If you don't mind throwing away(I would mind)the low end torque of the 3V then it is worth it. You can get lots of good parts for the 3V so you can make good power. You can get a Vortech supercharger kit for them too.