Measure the curvature of each piece to see which is the central one. That item, maybe short, has both the most super and the most consistent curvature. It's at the apex of the curve.
The outer pieces are those meant to impart an eased curve on both ends, so they will have both less super and either a gradual increase in radius or just a wider radius...not sure since I have never used the Unitrak. But, I'm guessing all this because of the footnote under the image showing the super-elevation. So, if you have three or more items to connect, there is one, or at most two (?) central curve lengths, and outside of those, on either end, will be increasing radius items with a concomittant reduction of super towards the tangent.
I want to assemble a curve going right. I have parts R790 PCR, PCL and PCAR. As i transtion what is the order of assembly. KATO's charts are confusing. Which part first? Second? Third?