Just found this topic by chance! Was this implemented in the end? If not, I previously implemented in R a solver based on Dario Izzo’s paper but modified to follow the design choice described by Gim Der to attempt to find all possible solutions for a given problem set up, i.e., covering all combinations of high and low altitude paths, and for all possible number of complete revolutions. I found that combining the good rigorous mathematical theory by Izzo with Der’s design of finding all solutions brings the added value that users do not have to input constraints such as maximum number of revolutions (I also tried to implement Der’s approach on its own but found the algorithm to be unstable under quite a few starting conditions…)
So if this is still an open issue, I can easily port it 