I floated the idea of putting a modest arch sort of transition at the joint. I checked the attic and the wall isn't load bearing - well it was a tiny amount - the roof rafter above it had a 3 foot small post resting on the top plate (not a steep roof) - the rest had one brace going from center of rafter over to the plate at the top of the common wall, the one that will stay in place - dining room on other side. So I added a brace. If I had needed to put in a triple 2x12 or something to support major weight, I'd have been off the hook for the seamless merge.

Oh well, should be interesting and I'll take pictures.

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1986 300SDL, 362K
1984 300D, 138K