I saw a posting on the Atlas HO scale forum that Athearn will be adding the MP-15ac to it's high-end Genesis line, and that NYA is a possible roadname for the run. Check out www.atlasrr.com and go to the HO scale forum. I guess 155 and 159 would be the units, since they are painted in the same color green, 151 being a completely different shade and 156 is still in LIRR blue and white.
here ya go. .
http://forum.atlasrr.com/forum/topic.asp?TOPIC_ID=14451