What would a modeler need to get to make one of these? I'm thinking of the Danbury branch through trains(1146,1148) just before metro north
Well, for that era you need a pair of FL9s painted in the old blue-yellow scheme, or in the two tone gray of the seven 1979 rebuilds; and 7 or 8 8600 coaches. Models of both the FL9s and the coaches can be hard to find --- not impossible but hard.
S. Soho made the coaches in brass about 27 years ago, and they do show up at brass dealers now and then. You have to look but they can be had. E&B Valley Car Works made them in plastic and later sold the dies to Eastern Car Works. The NHRHTA marketed those kits with Concord Junction sides, but they have been gone for a while. The ECW cars can be had too but, again, you have to search. Try some Google searches.
Regarding FL9s, two brass ones were produced twice: by NJ Custom Brass about 1983, and by Overland sometime later. They show up at brass dealers too but are undeniably pricey. Branford Hobbies (Connecticut) produces, or did produce, a kit with a plastic or resin (I do not know which) body.
Oh, one other thing: one of the Danbury trains in that era carried a bar car that was one of the batch of second-hand stainless cars from various roads that MTA purchased a number of in the 70s. That particular car had originally been built for Pere Marquette and later sold to Chicago & Eastern Illinois, MTA being its third owner.