Honestly....the largest vacuum source on a motor is where the intake manifold leads to the brake booster. Many after market vacuum blocks that companies such as FullRace make use the brake booster line as their vacuum source.

There are certain vacuums you want to try your best to avoid using...

One is MAP Sensor.
The 2nd is Fuel Pressure Regulator. If you end up drawing too much vacuum from your fuel pressure regulator it CAN mess up fuel pressure.