To round out the entries in this thread as to the differences among various train models:
The R-32's are in permanent or "married" pairs. Between the 2 cars in each pair, they are permanently linked with a link bar with permanent air and electrical connections. At the other end of each car is an automatic coupler. Internally, each car has 2 diagonally opposite corner cabs. The one at the end with an automatic coupler is fully operational, with controls that include driving and door controls. The cab at the married pair juncture hasaccesory controls and door controls, but no driving controls. At the married pair juncture, there are no headlights, taillight, destination signs, or windshield wiper. Underneath, only one car in each pair has an air compressor, while the other one has equipment for emergency power.
The R-42's are also in permanent pairs, but differ from the R-32's in that the motor cab lacks door controls, thus providing each car with a distinct motor cab and distinct conductor cab with the conductor working a car length off center on some trains. Also, the conductor cab doesn't have a pointless windshield through all that will be seen is the "blind" end of the other car in the pair.
The R-44's and R-46's were origially purchased with some cars having a full width, fully operational cab at one end and no operating controls or cab at the other. The other cars were motorized trailers with no cabs or operating controls. Cab, or A cars are even numbered with full equipment including an air compressor and back-up power while B cars lack those features. Originally, these cars were single units that could be easily separated and coupled up in various combinations - but they needed each other in that a cab car had to be in a consist with at least one other cab car facing the other way, and a B car had to be in a consist with cab cars. In the late 1980's, the R-44's, except for the ones on Staten Island, were converted into permanent 4 car groups consisting of a cab car at each end facing out, and 2 B cars in the middle. Some of the R-46s were converted into the same type of groups, while some were converted into married pairs of 2 A cars linked blind end to blind end, and 1 A car and 1 B car were made into a married pair.
The R-62's were all originally single units with full operating equipment, and an automatic coupler at each end with a fully operational corner cab at each end in one corner with driving controls and door controls on that side included. Many of them were converted in 1998-99 into 5 car groups, with 3 air compressors, 3 sets of emergency power contorl, and a full witdth cab at each end with full controls including door controls for both sides.
The R-68's were originally single units with a full operatonal cab at one end and a motor only corner cab at the other. They were converted into 4 car groups. As with the 62's, the intermediate cabs had the driving and door controls disaasembled or disabled.
The new cars ordered since the R-68's were always in 4 or 5 car groups.