Here is what the AMA has public on Mr. Rockwood, a very interesting read.
https://www.modelaircraft.org/files/rockwoodedwardl.pdf
There were other early tone systems, at least in theory, but Rockwood's system put steel fingers, each tuned by length over a single audio voice coil reducing the size and amplifiers required. I'm surprised that such a book would have been published in England during the war. I think RC was completely shut down here after 1942 to 1945.
On the spar issue, I know the theory is a slightly flexible wing won't fail... And part of that may be that bonding plywood to balsa was not that easy before epoxy glues, or that with a .35 engine you just don't hit the air loads. No doubt the silk covering enters into the equation. I will have to think about that.
Most Smog Hogs ended up as trainers as the '50's became the '60's. They seemed to gain weight with .45's to .60's and repairs. I remember reading of 8 lb. Hogs being not uncommon. Beginners have not learned restraint with glue or paint. I once helped a kid when I was in college fly his Midwest Trisquire with a a K&B "Stallion". It flew good, but then he took it home and repainted it. Afterwards, it barely took off and need 2/3rds throttle just to fly level. I had to burn most of the fuel before it would fly just below half throttle and landing at that speed was a thrill.
Interesting that a T-8 eight channel is for sale. Eight channel reed systems were rather short lived, appearing in 1957. The Smog Hog won it's second Nat's with ailerons with a 8 channel Orbit flown by Bob Dunham, owner of Orbit. The early demise of 8 channel reed sets was due to the lack of elevator trim. Ten channel reed systems became the standard by the end of the '50's, and as transistors improved and cost less, the heavy relays were removed from the receivers for transistor amplifiers in the servos.
I should note that some limited elevator trim change could be done by messing with the centering board that had contacting wipers that controlled the motor for centering. I think this was used to have additional down trim for inverted attempts, but am unsure of this point.