now have all 3/need extra couplers

What brand of passenger cars are they?

Lee Fritz

Lionel "baby Madisons"

General Mills, the breakfast cereal company, purchased machines, tools, dies and the rights to manufacture Lionel Trains from The Lionel Toy Corporation in 1969. Lionel trains were well known but they weren't selling - they had lost $13 million in 10 years. Some General Mills officials wanted to revive the line, and they did. They made Lionel trains under the auspices of Model Products Corporation (MPC). They introduced Fast Angle wheels and needlepoint axle bearings that reduced friction to nil. Locomotives could pull much longer trains. They also used state-of-the-art painting and decorating techniques to "eye wash" customers with cars that looked a lot better than older ones. 

Lionel's Bakelite standard/heavyweight/non-streamlined passenger cars were 60' Madison cars introduced in 1941 and made through 1950, Lionel's 50th anniversary year. There are two stories about their demise: (1) Their dies were scrapped during the Korean War; (2) Their dies wore out and they weren't replaced.

Lionel/MPC couldn't afford to make new Madison cars from scratch. New cars would have to run on 0-27 track, like other Lionel/MPC trains. CN heavyweight cars in Toronto were measured. Mockups were made of light plastic, not Bakelite, and compressed for 0-27 track. The first set was the BROADWAY LIMITED in 1973.

These short, light cars have been made ever since. They were not called "baby Madisons" until years later. That name distinguished them from Lionel's reissued 60' Madison cars and longer "scale" heavyweights.

In the same way, "PS-1" was not used until MTH introduced PS-2 command systems. "PS-1" filled a need for a concise designation for earlier products.