I won't be doing the reboring myself. I thank both of you for your insights. I wondered if there were a reason why I hadn't heard of more people modifying these old rifles. I never considered the balance and recoil, I still want to follow through with this though, whichever caliber.. I was quoted at around $500.00 bucks for the boring and minimal reworking of the reciever for .375 H&H. I probably ought to jump on that. The stock has been chopped and will need to be upgraded. So I won't be destroying a nice piece of history. Who knows, If it does have enough metal to bore out to .416, It might be a little easier to lug around. The thing must weigh about 12 lbs.
Believe Ten percent of what you hear, and Half of what you say.