Regarding the listen back mic, I'd reseat the 33 cards in the 651. Then I would swap the two cards over.
The 33 card that's at the top (after the oscillator/34 card) does Talkback, the next card does the 2 listen mics
I'd rechip the 5 Op-amps for maybe a quick fix. It's largely passive/apart from the caps after that.
Failing that it's extender time.
Regarding Spectra, with a 24, I guess you'll get one side.. personally it's a bit crappy as a tool.