Peter,
I see one major, and a couple of minor problems ...
The datasheet for the LM2940 regulator specifies that a minimum value of 22 mF must be used on the output terminal ... or instability will occur. You can change the value of the capacitor, or just add a 22 mF tantalum cap to that output terminal.
Your '72 CDI uses nothing but a 33 Ohm pullup resistor as a switched load for the points, so minimal transients [no inductive spikes at all] will be present on the input ... so the two diodes on the input line at pin 1 of the IC are really not needed, or you could put a single SA15A Transzorb (rated at 15 Volts) there. The 12 Volt Zener could actually introduce switching noise into the circuit rather than eliminate it from the signal!
The transient protection and hysteresis adjustment circuitry are probably superfluous because of the Voltage regulator IC, and I suggest eliminating those components until you have the 'basic' speed switch circuit (fig. 9) shown on page 8 of the application note below.
Likewise, I suggest driving the LED or lamp from the output terminal 8, so you can eliminate the PNP transistor and its' bias resistors.
Once you have a working prototype when connected to the ignition system in the car ... some probing with an oscilloscope should be able to tell if any noise or transients are present that need to be taken care of.
