Ok, I'm willing to put in some legwork on this one, but need a little help. It appears the transistor module is just 3 ignition modules packaged together. I am working on drawing up a wiring diagram to show this.
According to TM1591, "The ignition circuit is made up of three separate circuits, one for each cylinder. Each spark plug has its own separate pulsar, transistor switch [located inside transistor module (A2)] and ignition coil. This system eliminates the need for a distributor."
Seeing as these engines are meant to run at a fairly fixed speed, combined with the info in TM1591, I am fairly confident there is no timing advance circuitry in the transistor module.
This means we should be able to use a standard packaged transistor switch, for example, a LX301 (GM HEI ignition module).