If the alteration you are thinking about can be done, it would be a major and costly project. I would get the opinions of at least 3 different fireplace experts. If they all agree that it can be done, and on how it should be done and the cost, then it's up to you to decide whether you want it badly enough to spend the money and live with the mess while they're working. But if even one of the 3 experts advises against it, I would not do it. You do incur a risk of "expert" opinion that is wrong (not so expert), or worse, a so-called expert who is just looking to make some money, and he can't make money if he says it can't be done. There is also a risk that, once they start the alteration and dig into this or that, that they find womething they did not expect, and they tell you that it will cost more to do it because of the unexpected finding.

You might also check with the forum in hearth.com. The people there love and breath fireplaces. You might get some interesting opinions from them. I wonder if they would agree or not.

Thanks, Haus! You verified what I was already thinking. I wioll however cross-post the question as you suggest-just for fun. Thanks again.