Dimension A is easy enough to foreshorten but I can't get Dimension B. I tried getting dimension on main view and holding shift to drag it to the detail (another thread) and it won't work properly because it's for the o-ring cutout rather than the outermost dimension. Thanks.
Raymond,
I opened your files and used the same procedure I described a couple hours ago. I deleted the dimension you had inserted from the tangent line, activated the Smart Dimension tool, and clicked on the two parallel edges shown below (clicking on the one in the Detail View first). As you can see, it worked fine. I don't know why it doesn't work for you if you did the same thing.