Marking a 2 lines to create a 3D line ?

Hi guys,

I want to remove material from wall A and wall B which curve and change height along the marked lines 1 and 2.

Lines 1 and 2 are seperate lines which are coincident. Is there a way I can convert them to a 3D line so I can use that line to create 2-3 sketches of the "material removal" along it and loft cut?

Thanks!

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