Heat expansion of copper could be worse that the Aluminium....not sure.

But i reckon the heat should burn up any rust/oxide stuff in the gaps.

I've been meaning to buy a blow torch, I'll give it a couple more attempts with the rust eater and the vice grips, then a 'heat' solution, then belt the absolute #### out of it, then drill it to death.

That should just about cover it I think - I'll stick the solution that worked on my webpage when it is done.