Another amazing post - I was most facinated with the part about heating bore sized metal rods and placing them in the barrels to aide in regulation. It may show my ignorance, but I have never heard of that technique.
If I may ask a question: Can you please share, in this thread, the background on your decision to have this individual build you a .600 DR?
Why a .600? (not that I'm questioning it, I would like one too one day - that is, after I have shot my .577 a few hundred times ;-)
Do you have a piece of wood picked out for the stock?