I wrote a MATLAB script that takes as input the measured distances and produce the optical path lengths. The script also produce a drawing of the setup as reconstructed, showing the measurement points, the mirrors, the reference base plates, and the beam path. Here is an example output, that can be used to understand which are the five distances to be measured. I used dummy measured distances to produce it.
This path does not look correct to me. Maybe it's because this is supposed to represent "optical path lengths" as opposed to actual physical location of optics, but I think locations should be checked. For instance, PRM looks like it's floating in mid-air between the BS and ITMX chambers, and PR2 is not located behind ITMX. Actually, come to think of it, it might just be that ITMX (or the ITMs in general) is in the wrong place?
Here is a similar diagram I produced when building a Finesse model of the 40m, based on the CAD drawing that Manasa is maintaining: