Well if your coolant gets to the oil and they is being burnt, it means you oil is too!!!
If you are happy with the head job, its more likely the turbo where the problem is arising.
For lots of white steam smoke, it must be coolant getting directly into the combustion chamber or inlet tract.
HAppy hunting. BTW, what were the symptoms and circumstances of your HG failure.....? It is very rare for a 18T HG to fail, even when mapped. UNfortunately once the head is off them, in my experience, they are never quite the same again for some reason!