More mockery, sorry, mock ups!
After some amazingly helpful suggestions over on NGRM, I am getting closer to a final plan. Now, different levels will be incorporated, with the OO gauge tracks on the highest level. The NG will now have its own fiddle yard built into the asphalt filling shed, and the trackwork has been realigned near the beginning of the jetty.

The above photo shows the current state of the mock ups, and also includes a diagram showing the potential for another siding to serve the powerhouse. I need to see if this is feasible first, because I don't think it will look right having the NG appear and disappear under the standard gauge twice. If this is done, I will need to completely block these entrances! It is always worth trying out new ideas, though.