For a 79 porsche 911 targa, Where does the #1 spark plug start from on a distributor cap from a vaccum guage?

Answer 1

That is a bit difficult to say exactly.
Do this:
Rotate the engine until the #1 Cylinder is at the top of the stroke after the intake valve closed. this is TDC. Pop the cap and see where the bug is pointed, taking into account the direction of rotation of the Distributor will give you the exact answer.
If you are asking if this can be read from a vacuum gauge, I would have to say NO!