Hi Phil- I think you do have the ports - I’ve circled one in red.
To use them, you have to remove the plug and screw in something to attach a vacuum line to. I think they’re m6 threads.
But I’m not recommending it!
For the dizzy work -
You take your distributor apart - just some screws for 240z, 260z to lift the breaker plate out, A bit more involved on 280zx but still not hard.
You’ll find under the plate a thing that looks like this:
You can see a spindle with arms and slots in the arms. The breaker plate attaches to the top of the spindle. The pins in the slots are attached to the weights underneath. As the dizzy spins faster the weights move out, so the pins move out too and in doing so they rotate the spindle that the breaker plate is attached to, advancing the timing.
So you add about 2 or 3 mm of weld on the outside of the slot, reducing the amount of advance it can add.
Then you reassemble and run the engine. Point a timing gun at the crank timing markers with the engine running and you’ll see advance increases as you accelerate the engine. It’ll reach a max at around 3500 rpm. Twist the dizzy so that it shows 34 degrees advance at that max.
Now let it return to idle. If it shows 15 - 20 deg of advance now you’re probably done.
If it’s at the high end you might have trouble starting. So let it go cold again and try to restart it. If it starts then your done. If it doesn’t you need to open it up again and file a bit of that weld away so it can advance a bit more. Repeat.