Susan,
I think the cars for the Blue Line and Orange Line are essentially the same. The older cars are the Hawker-Siddley cars from Canada. The difference being of course the pantograph for the Blue Line for the surface line out to Wonderland.
This line was once the "Narrow Gauge", or the Boston, Revere Beach, & Lynn, which once ran Mason Bogey 24" steam locos with heavyweight Laconia parlor cars! Later on they electrified with the help of General Electric and put trolley poles on the heavyweight cars. When they went out in the 1940s, the plans were to incorporate their system into the Boston Elevated. This happened in the 1950s when Logan Airport opened.
The Red Line cars are much bigger, in fact some of the widest and largest subway cars in the world. This is a relatively new line, which was built in the 1910s. The original line was called the Cambridge Subway.
Now if we could find some Hawker-Siddley cars, I could easily reskin them. This is an easy task compared to making something from scratch, which I'm not good at either. My brother can, but he's busy with other projects at the moment and wouldn't be able to do it in any reasonable amount of time.
John