Would be tricksy. Probably need to convert back from Coil pack ignition to dizzy (AU's used coil packs afaik
). Also need different injectors or computer mods to cope. Other electrical compnents (sensors etc, might also be incompatible from the AU to the EF ecu's)
As cogo said, would need reasonable loom changes as well.
It might be easier (not sure on price), to investigate an aftermarket computer for running the motor, and leave the original ecu for smartlock compatibility and so forth.
I'm also unsure about the transmission compatibility (I *think* V8's used 97le, and 6's 95 or 93le) - not sure how different they are. If manual, you would need to change boxes (different input shaft lengths). This *might* entail other changes, perhaps driveshaft (probably not I would guess).
All in all, I'd seriously consider just buying a V8 (not what you want to hear :) ). You could also realistically push the I6 to similar or higher power levels for the same money as the V8 conversion. (e.g. turbo / s/c).
A big job, with lots of investigation to do (don't take my word as gospel on anything except the need for LOTS of investigation before you make and decisions or spend money). Good luck