Ken, guys like me really do appreciate the way you show the details of your build. I seem to have the same problem with my rad, it runs the same temp ranges as yours. My expansion tank has the two holes in the bottom one flush and one with a standpipe. I figured the line from the rad cap goes to the lower opening but I don't know where to run the return from the standpipe. I've just left it open so far and it does boil over and leak out never returning to the rad.
What I gather from reading your thread is I have to run a line back to the cap some way and not just let it leak onto the street.

Sean