Frank, that is exciting! I have been wanting to build this myself. I did build the right-hand 4X8 as my Cisco RailRoad which was an article in OGR. But I have not built-out the left-hand 4X8, I extended the layout with a 4X4 section, along the lines of below. I wanted a siding for the Menard's Power Plant but did not have more of the room to expand into at the time.
I hope you will post pictures of your construction.