Pat, I don't recall the inner-to-outer cowl (that's what the vendors call them) that I bought had that notch you're referring to, but I can't be sure. It would be to provide a little clearance for the inner (kick) panel flange and the flange on the floor that bends down vertically. There are 4 thicknesses of metal there, the floor flange, the inner cowl panel flange, the rocker panel and the inner-to-outer cowl piece.
A little slice there would take care of that. Cut vertically with a 1/16" cutoff tool, tap the tab outward and weld it back to the main part of the cowl.
On mine, I rotated the whole thing enough that the indentations fit around the beads on the inner cowl. I believe I wound up cutting off what protruded out the front. I also had to slice the top up to match the outer cowl so it was similar to your second to last picture.
Those inner-to-outer cowl pieces are notorious for having to be cut to fit correctly. I don't think you'll find ANYONE who had an inner-to-outer cowl piece that fit right.
I think you're on the right track.
