From what I have read, the transistorized ignition unit is beneficial if you are to use points; It stops the points from burning up. the 123 ignition systems does not use points.
My 3 way vacuum control value is controlled by the relays and it does work. however i have modified my throttle control by drilling a hole in the same place that the non emissions controls car have the vacuum hole. I can switch and run the car as a 1970 or 1969 system. with the 1969, provides fully vacuum at idle and it goes to no vacuum as you accelerate. So currently with my 123 ignition I am running it as if it did not have the emission controls.
I can also run it by changing the vacuum line at the throttle body (which provides constant vacuum, and this vacuum then goes to the three way value which gets turned on and off via the emissions control relays and it adjusts the timing on the distributor. This seems more likely to fail , (extra components such as the 3 way) and its why I wanted to run it without all that stuff.
I hope that helps. but please correct me if I am wrong on the use of the transistorized ignition module.
Regards
Pinder