Paul
That 8.47 dimension is to the small vertical front end of the rocker panel. See the attached pic.
As far as lining up the holes, that dimension to the front of the rocker is the only thing that will get it correct. if you have the rocker too far back, and line up the holes in the inner-to-outer cowl panel, it will still be too far back, as the inner-to-outer cowl will also be too far back. The inner-to-outer cowl is located by the rocker location and not much else.
Yes, I've definitely been there, and have the t-shirt.
