I do not think that Athearn ever made U-boats with plastic handrails...If it is Atlas you are talking about, I highly doubt it. Stanchion placement is not even exactly the same as the Dash 8's and 9 let alone other GE locos that whose prototype years were not even in the same decade. If I were you, I would maybe look into buying an Athearn "blue box" C44-9W handrail set and modifying it into what you need; should be a pretty close fit and will at least have the right amount of handrail stanchions.
If you're really serious about this project, you have the money to spare and a good amount of patience, you could also try a handrail set from Smokey Valley. Not sure that you've used a set from them before, but they are not for the faint of hearted. On the other hand the results are to be unmatched in accuracy!
Again, hope this helps! If you wouldn't mind me asking too, would you mind sharing your details about this Dash 8 you are going to build? Not too many people out there building GE's...Always nice to hear about what everyone else is doing.
-Rich