[38 coupe]

There is no need to disconnect the vacuum line. The factory vacuum port on an 8BA is a mix of ported and venturi vacuum. There is no vacuum in the line at idle.
I typically set the initial advance with the engine off. Rotate the crank until the pointer is lined up with the bump. Pop the distributor cap off. Loosen the distributor hold down clamp. Turn the ignition on. Retard the distributor until the points are definitely closed. Slowly advance the distributor until the points just open (the points will spark when they first open, usually I have to do the retard and slowly advance a couple times to avoid over advancing). Tighten the hold down clamp without letting the distributor move. Turn off the ignition. Reinstall distributor cap. Timing is set.