The heaviest train I ran on the NYA (although not the longest) was 40 loaded TLTX cars for Prima, 15 loads for Arriva concrete and one lonely reefer car in the middle for Mid-Island produce. 56 car train, not the longest, but definitely up there in weight. Power was 3 38's and 1 MP15ac.
The longest train I was conductor on was around 63 cars earlier this year. Power was 3 "overheated" 38's. A crap load of paperwork to fill out on a train that size