Ray,
You need a center rail break and each end of a block.
I use a 3M professional electrical tape wrapped on the center rail contact of each track, the springy looking thing, to create an isolation point. The previous builder of the layout that we are restoring cut them off or cut rails, causing us to replace the tracks. I had to isolate the helix from each level for 3 level running control or we can switch back to all levels running for one train.
kapton tape would be another tape to use. Both are very flexible.
So, the five inch pieces where they fit or the tape will work fine.