If it was me, i would opt for around the walls as your benchwork red-lines indicate. Do you need all this empty space in the center of the room?
Thanks for taking the time to reply to the thread. Adding the two spurs did a little in the center of the room. I have a feeling that once I start erecting the benchwork I may decide on tweaking it further, however I do know I don't want a duck under. I also like the idea of some "roominess" and very much do not like a cluttered feeling.
I agree with going around the perimeter, as the walls along the sides are only about 4'2" at the outer edge and slope up at the 10:12 pitch so eventually by 2 feet out will be able to stand up comfortable. Where as the other option I considered one would be bumping their head or there would be a lot of wasted space in the perimeter.
One simplyfing factor, I believe, is going with track that was actually in place during the era; which makes planning in the towns much simplier.