RCA BTA-1R1 circuit questions; undoing modifications, etc.

So, I'm getting ready to turn this beast on again after it's sat for a decade. As I've pored over the thing, it's pretty easy to tell what's original...and what's not. RCA was very consistent in types of connections and crimp terminals.

The circuit itself gives me a couple questions, and then understanding a couple mods...

Background on the stuff I have and how it was supposedly configured... two RCA BTA-1R1 transmitters. They have sequential serial numbers. One is labeled aux transmitter. Added to both is a copper strap across and out the bottom, up the side and across the top, where it is bolted under what I believe to be a 1/2" coax flange (worm clamp/slit copper tube). A piece of copper strap is there to connect to the coax center conductor. I am not sure what was gained with the strap, the cabinet is a much much bigger flat aluminum strap... I am working with the aux transmitter as it has far fewer mods and clearly was used less (fewer replaced components and less heat damage). The main transmitter has several big changes on the output network.

If you look at the output schematic below, you'll see a double pi with a harmonic trap between them. All inductors are tapped. All capacitors are fixed.The first/main inductor is also slug tuned from the front panel (the adjustment is not stable/too loose/gravity retunes it, but that is another issue). According to the manuals on BAMA, upon install one would select the caps from a chart, select the taps and then adjust them while setting it up, and that was that. On the main transmitter, three big things were added: The first tune capacitor was replaced with a big vacuum variable. The second pi inductor was replaced with a Gates 15uH roller inductor. A large changeover relay was installed, with labels indicating it swapped the main and aux transmitters between the antenna and a dummy load.

First question: Why make the main transmitter output network so adjustable? The unit ran on one frequency its whole life. It has ConElRad features, but it actually ran ON the ConElRad frequency (1240kc) so nothing was needed for frequency hopping of any sort. Also, the vacuum variable and the roller adjustments were inside, all the interlocks are in place, so it was not likely something somebody tuned daily. What was being gained here?

Second question: what do you think of the changeover being used as an antenna T/R relay?

Next: the drivers. On the other schematic below, there's the RF driver, a 6146 in class C. You'll see it drives the grids of the finals...through IR326, a 100 ohm resistor to the first grid, and then IR327, another 100 ohm resistor in series to the second grid. Third question: Why? and, Wouldn't that make the two have slightly different drives?

In the audio section, there is IR501, a 6300 ohm resistor leading to the plates. In the aux transmitter only, this resistor is shorted out with a jumper. I'd expect this to raise the plate voltage, thus the amount of available drive to the modulators. Fourth question: Why?

The third schematic bit is IT302, the dual secondary filament transformer for the modulator tubes. There is shown IR303, a variable to choose a balanced center point for one of the modulator tubes. I am guessing this is for hum balancing. There is nothing I can find in the manual on how or when to adjust this (there is another hum adjust pot and the manual does go through adjusting it). Last question for today: Any idea what this adjustment process is?

Really the last question.... The manuals on BAMA (and every other manual I can find online, which are all the SAME scanned manual based on the handwritten notes in it) are wonderful aids, but the schematic and photo diagrams are not clear. If anyone has or has access to a paper manual they are willing to sell or scan or photograph, I'd be very appreciative. Along that same line, if anyone has clear photos of the stock insides of one of these things, that would be helpful. I am especially interested in the wiring around IK302 and IK602, which have been replaced and rewired with non-original parts in both of my transmitters. Given that the main transmitter also has a panel with 8 octal relays and a bunch of wiring going all over the place from it, I don't have faith that the replacements were just replacements...

All ideas are welcomed, I want to understand how it was supposed to work before I start hacking it up....

Ed