L-Jetronic Fuel Injection and Distributor question, Intake Manifold Vac Ports to/from distributor Options

[Str1974]

I have a 1974 1.8 L with a current Bosch distributor (0 231 181 009). I have two vac ports on my throttle body , one that goes to the distributor (vac retard) and one that comes from the distributor (vac advance) back to the throttle body.

I'm replacing my old distributor for a new 123ignition w/Bluetooth adjustment. The 123 dizzy has an optional port on it for a vac line, so therefore one of my vac lines going from and towards the intake manifold would need to be "capped". I'm hearing that I could either chose to cap either the retard line or the advance line or all together cap both ports on my intake manifold and choose to run my new dizzy without any vac lines.

I've also read that "The 914 distributor has a centrifugal advance built into it. This mechanism causes the distributor timing to change as the engine's RPM increases. The advancement of the timing is necessary because at higher RPMs, the engine needs to ignite the fuel earlier than at idle. In other words, if there were no centrifugal advance, then at higher RPMs, the full force from the combustion would impact the cylinder when it was already through the major part of it's stroke. This would result in lost power output. The centrifugal advance changes the timing so that ignition occurs earlier. Additionally, the fuel injection may advance or retard the timing based upon the vacuum pressure from the engine."

It's this last line from above that has me wondering how vacuum pressure from the engine works if there are no vac lines going or returning from the dizzy to the intake manifold??? Or , am I completely wrong that the vac ports on the intake manifold / distributor has nothing to do with it.

I'm still a novice and would like to understand more about this topic, or at least be less confused....