if its done correct before some other butcher has got to it. I've done it heaps mate????

Go inside and have a wank. Then ring ya mates and go croozin in their Hyundai. f**k yeah. Lets get some KFC.

I wouldnt mind doing this. Ha.
But would the heat of the welding f**k with the alloy?

Not in that area. Once welded just cool it down with a wet rag and youll be fine. Definately try giving it a good crack on the head as it can make all the difference if you havent tried it yet.

welding sounds like the best suggestion but,i do have one idea.Repco sell a spray by loctite we use it at work on bolts nuts and other stubbon parts to move,its an anti freeze spary you can spary it on the bolt where the head is and then where the thread is and let it set for a minute,this freezes the bolt and makes it easier to crack.
Your best bet is to get a 10mm single hex socket probably a 1/2inch size,hit that on with a hammer,then with a 1/2inch breaker bar,really give it a good yank to crack the bolt.Just make sure you fully spray the entire bolt where you can get to it.

then if all else fails weld it.