I don't know the lengths, but when the brake shoe is touching the drum, the lever in the middle (at the former cross-over shaft) should be leaning rearwards only a tiny bit just to compensate for some wear. If the lever points forward or rearward too much, you loose some leverage force and the brake feels soft. The closer to 90 degree from the pivot point to the rod you can get it at the moment of braking, the stronger the leverage and force you can put on the brake. That goes for the rear wheel lever as well, but I think it is no splines on that, just one fixed position?

What I can see on pics there is 3 clevises on the rods and they have about 1/4 to 1/2 inch of spare thread at the ends for wear adjustment.

The middle lever might have 2 hole options for the rear rod and gets the most leverage force from the pedal if it is in the upper hole, closer to the shaft. You can brake harder that way. You might need that on occations...

Contact Point No.434 Nov.5 1931 talks about for 1932 the regular light sidecar for Scout will fit both 45 and 74 as the sidecar chassis will be the same for both. It continues with that for the Four, both light and heavy duty sidecar is available. If the Princess was regarded as the regular heavy duty sidecar, it means that the Sweetheart was still sold. And it continues with that a new brake (mod. front brake) is available for all Indian sidecars.

For the commercial sidecars, a lighter chassie than the rugged heavy duty chassis that was "built like a bridge" is available for the 45.