In the late '40s the New Haven Railroad began taking deliveries of new stainless steel streamlined passenger equipment. None of this equipment ran on the Highland line. Instead, it was a mix of heavyweight and streamlined light weight (American Flyer) cars. At this point I am only referencing passenger equipment that would be found on the Highland Line.

There were no sleepers on any of the Highland Line passenger trains. An occasional diner or more likely a grill car appeared on special trains like the Narrangasset Race Specials. There was a lot of mail and express traffic, however.

Head End

2760-2766, 2768-2772: 60' Baggage and Mail (30')
2780-2789: 60' Baggage and Mail (30')
2790-2794: 60' Baggage and Mail (15')
Assigned: 131/136
3800-3946: Baggage

Heavyweight

600-658: Converted Parlor Coach (CvP)
These paired-window coaches were rebuilt from 2000-series parlor cars specifically for commuter service on several lines, including the Highland. All of the cars have 88 seats, except 601, 607, 609, 610, and 611 with 84 seats.

In the Shoreliner article there are two plans shown. These were converted from at least 5 different parlor car plans. In addition, the window spacing on plan 9401 in the article does not match that in the photographs.
 
6800-6823 Deluxe Smoker
 
8100-8104, 8107-8139, 8151 Coach
 

Light Weight

The New Haven Railroad started taking delivery of new streamlined light weight passenger cars. These were built by Pullman Standard at their Osgood-Bradley plant with a low-profile riveted construction and turtle roofs giving them a smooth, streamlined profile. They are commonly known as "American Flyer" cars, because of a line of S-gauge model trains marketed by the AC Gilbert Company of New Haven, CT.

These were the last passenger cars added to the roster until after World War II and the delivery of the stainless steel streamlined passenger cars.

8200-8249: Coach
8250: Coach
8252-8269: Coach
8270-8299: Streamline coach (SL)
Assigned: 421, 463
8300-8349: Coach
8350-8369: Coach
8370-8374: Coach
8500-8529: Streamline reclining seat lounge coach (SLrL)
Assigned: 128, 129, 131, 136

Resources
On the rear cover of Shoreliner magazine (Vol 30, No. 2) is a picture of Business Car #1 (The Yankee) taken October 30, 1954 in Plainville. In one of the Arcadia Books is another picture of Business Car #1 (based on the railing) at New Britain Station.
Shoreliner
Volume 21, Number 3
pg 8, "Butterflies to Caterpillars."
 
Baggage Assignments
 
Mail Assignments
131, 136 
 

600-Series Coach Assignments 

  • 5/49 - 4/52 - 6xx - 421, 444, 446, 450, 463, 472
600-Series Models
  • 603
  • 610
  • 613
  • 619
  • One from 639, 642-647, 650-656
I'm modeling at least 5 of these cars, one for each plan. I have not found left/right photos for any single car from Pullman plan 3917 so I haven't decided on a road number. But there are left/right sides from a number of different cars.
 
Peter Ness presented a clinic about converting the Walthers parlor (932-10300) to cars 619 and 627-637. I'm basing my conversion on his and have two of the cars underway.

Branchline Steel Coaches
 
6700-6725 Rebuilt Smoker
6824-6843 Smoker
7800-7950 Rebuilt Coach
Including the 4-wheel truck version for 7922, 7929, 7932, 7935, 7936, 7938, 7939, 7942, 7943.
 
The best starting point for the NH Heavyweights is Branchline Trains excellent single-window coach model. The fishbelly underframe needs to be replaced, and the rivet plate details between the windows aren't 100% correct, but the window placement is very close to the New Haven prototypes.