I dont recall hearing of this electronic switching test at Morris Illinois before. But Google has, it is mentioned when you Google Morris Illinois.
http://en.m.wikipedia.org/wiki/Morris,_IllinoisI dont know how the experiment was done at Morris but AE Canada tested their very first electronic CO, the "C1" (and yes, everything that I have been told does indicate that "C1" means Canada's First electronic exchange) at an existing CO on the outskirts of Vancouver in an area known as Whonnock.
This was a few years later in mid to late 1960's, maybe 1967 and special phones were not required by then. During the test which went on for somewhere between one and two years, the existing SxS CO and the new C1 CO were cut back and forth several times. At the conclusion the C1 exchange was removed and sent back to AE in Brockville for further examination.
I would expect that a similar situation existed at Morris. They would not likely have cut this CO in and removed the old one as in a normal CO cutover. They quite likely cut back to the old CO some time after the experiment concluded though maybe others have more information.
I would expect that these special phones that were required for the new CO would have been made to work with the existing CO as well if at all possible. So thinking out loud about the lamp...could it be a resistance lamp in the ringer circuit to possibly make the phone compatible with the existing CO at Morris as well as new test CO? Cutting a CO over quickly is one thing but having to replace all phones simultaneously is another! Making the new phones compatible with both Exchanges would solve a lot of "logistics" problems.
They couldn't install these new phones in the subscribers house until after the CO cut over to the new electronic exchange if the existing CO ringing would damage these phones. That would leave the customer out of service for some time or at least unable to receive calls until the phone was switched out.
Terry