[Arran]

Mr Fix;
I have seen power output tubes used in parallel in some Canadian Marconi battery sets, one of the other features they had was an "economy" switch on the rear which would turn off the filament on the second output tube. However this Silvertone does not appear to have such a switch, my guess is that the choice of wiring the 1E7 in that way was so they could run it in class A, rather then class B, and forgo using a step down audio interstage transformer. It also simplified the circuitry, and the operation of the set having one B+ voltage of 90 volts, which also eliminates that third "B" battery. I suppose one could "hot rod" the audio amp, since someone apparently clipped the battery cable off anyhow, adding an extra wire, and voltage is no big deal with a battery eliminator.
A lot of Sears sets were made by Colonial, which was a S & R subsidiary based in Buffalo, New York. Colonial was formed out of the remains of King Hiners, after the latter got into financial trouble. King Hiners was already a Sears supplier, so I guess they saw an opportunity for what they now call "vertical integration". Another supplier was Stewart Warner, who apparently built whatever Colonial could not supply, there are a few examples of mid 30s gold dial models that were built by both companies, but the circuitry was slightly different even if the model number was not.
Getting back to the speaker, maybe some members could keep their eyes peeled at the junk pile at some upcoming swap meets, such as a similar Silvertone with a damaged cabinet? You and I are two of the few that will even give these sets a second glance, monetarily they will never be worth as much but their performance may surprise a lot of people, even the 40s era ones.
Regards
Arran