You essentially need to meet all the government regulations for your model(XE) car as a V8, if you upgrade to a V8 motor you need to have breaks and suspension that can handle the extra wait.
I ain't a mechanic mate, so i can't give you specifics on what is involved as yet because I havent seen it all unfold, so far we have only taken the 6 motor out of my Fairmont.
That involved removal of every engine component and ancillary along with the removal of the dash, computer etc etc
Essentially from here we are simply going to bolt the Xr8 driveline into my car and marry up all the connections.
The good news is the loom comes through the firewall in the same spot as the 6 does, as does most of the other functions such as the heater hoses.
Be prepared to either spend alot of your own time and that of your mates or pay someone alot of money.