So, being a glutton for learning (or at least, confirming), I pulled U49 (the hex inverter), and breadboarded it with a +5V rail, and ground (from my bench PSU), then fed it a 5Khz 5Vpp square wave to the 4 inputs I could see were used on it (guess I could check the two unused ones, but why?). For interest, I set my FG to HiZ "destination" (50R source), put a Tee on the output, and put one output directly into channel 2 on the scope (blue trace), and the other half of the T goes to some minigrabbers that I hooked to the input/gnd.
Something is DEFINITELY wrong. Two of the inverters (1A and 5A) give basically no output (although it still looks capacitive), one (2A) gives something that definitely looks capacitive, and the other output (3A)... god, hell if I know what it's doing. I do know on a couple of the inverters, when I'd feed it a signal, the IC would draw about 30mA of power. On the other 2, it would draw about 10mA. I do know the 3A output was basically what I was seeing in circuit (drives the strobe channel).
Also of interest, all of them seem to either offset the input voltage, drag it down, or completely destroy it. This could be my fault for not understanding something required... maybe the FG can't drive enough... but I would think the inverter inputs would take VERY little current to drive.
Definitely failed.