chewie8han: I do note the term "subway locos"--Subways don't have locomotives. Generally all cars are powered with their own electric traction motors via third rail, so there is no "loco and cars", just a series of cars.
If you haven't been on a subway and want to model one, GO LOOK AT ONE. At least look at photos of subway cars and compare them to an RDC. One thing mentioned above is the doors--subways have multiple sets of sliding doors mid-car, where RDC's have single doors on each end.
I can definitely see where you're coming from in the "fluted stainless steel" department--but there are some real differences too. Subway cars are typically short or articulated to get around tight curves--that 9" curve mentioned above isn't an exaggeration, in fact it seems a bit broad!
One thing you might try is a modern LRV model (There's some company that makes one--IHC?) with the pantograph removed (power pickup would theoretically be by third rail anyhow.) It's not stainless steel but the body configuration would be a lot closer.
But enough about the car itself: how are you planning on modeling the subway? Side-cutout views of station platforms? You mentoned "L Train"--I assume you mean elevateds--are you planning on having part of the line be subway and part surface or elevated?
In any case, get yourself to the nearest city that has a subway or elevated line. If you can afford a trip to Chicago, that might be very helpful--they've got both, as well as a big ol' HO scale model of the city (at the Museum of Science & Industry) with models of both, plus a hatful of hobby shops!
Close-up views of subway systems, as well as the cities where they are used, will prove invaluable in modeling such things--bring a camera and a notepad!