Replacement mortar question

Hello all
I have a small question about replacing mortar in an old brick wall (about 100 years old). The wall in question is a 2 wythe load bearing wall that used to be the exterior of the house, but ~50 years ago an extension was built. As a result, the wall is now an interior wall.
When exposing the wall (it's in good enough shape to keep as an exposed brick wall), I noticed that there is a section of missing brick about 1 sq ft (clearly intentional). There are also a couple loose mortar joints, etc.
To my question: I'm looking to mortar in a couple of bricks and repoint some of the joints. I've heard that for extremely old brick type O mortar should be used. However, this is a load-bearing wall that won't encounter any weathering issues - should I use type N instead?
I'm not worried about color matching, the patched area is not going to be one of the exposed areas. I am concerned about load, as I am going to be cutting a doorway into the brick wall and putting a header in, so the patched areas will experience somewhat increased load.
Any advice out there?
Thanks
Paul
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<snip>

You want to use weaker mortar for older bricks becuase you run into trouble if the mortar is harder than the brick. Since this is an indoor wall, use the softest mortar available, since it's the weather that does in mortar. Don't worry abou the strength: for one thing mortar strength contributes nothing to the overall strength of a wall and for the other thing: the wall was doing it's job just fine with the bricks gone, wasn't it?

If your design depends on the mortar to hold up, you've done something wrong. Historically, mortar was nothing more than three parts sand to one part lime: no cement whatsover, and it held huge loads just fine.
John
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Paul wrote:

wall or you might have the whole thing fall donwn on you???????????
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Bull Shit. If a building engineer comes on my property, I shoot him/her and ask questions later.
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Hope your header includes a steel lentil if there is brick above to hold up....
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