The Images of America series of books has a great book called "Boston's Red Line - Bridging the Charles from Alewife to Braintree".At the top of page 25, there is a shot of the Eliot Square rapid-transit shop yard. About two-thirds of the way up the photo, there is a concrete wall that separates the yard from Boylston (now JFK) Street. There are five or six massive doors in the wall that can be slid aside to allow passengers to enter from the sidewalks. On the yard side of each door there are two sets of stairs that lead down to the boarding platform. That was Stadium Station.
Not maps per se, but I thought that you might enjoy these three metal order of station signs from the three lines in my collection;
1954 Revere Extension (Blue Line):
http://i203.photobucket.com/albums/aa26 ... oad009.jpg
1928 Cambridge-Dorchester Line (Red Line):
http://i203.photobucket.com/albums/aa26 ... d007-2.jpg
1919 Main Line (Orange Line):
http://i203.photobucket.com/albums/aa26 ... oad010.jpg
These were installed in vintage rapid transit cars of their respective periods, usually by the doors, and were found to be an easier way to determine stops than maps, which is why newer versions are used to this day on modern equipment.
(As an interesting aside, most of the Revere signs escaped the collectors as when the Pullman cars were re-painted, the signs were reversed inside the cars, so as to present a smooth, finished surface. After they were painted over, most of them hid that way right through the end to the scrapper. You can see the light blue paint on my sign that ran in on the "backside". Ironically, the air-sealing effect of the coat of paint preserved the signs in the salt sprayed air of Eastie.)