With the key on, see if there is a voltage drop between the distributor body and the battery negative post. Also, if you just need to get it running, splice the wires with suitcase connectors (aka tap splices, Scotch Locks). You don't have to cut off the connectors, and you can pull the splices back off later when you fix the plugs.
6V is completley normal for a coul during cranking, esp if your using a Digital Voltmeter. there is a constant fluctuation of 12V to 0 V then back to 12V and this happens very rapidly. why?
ignition coils basically make power. the 12v is used to create a small magnetic field around a winding of coil. once the power is cut off from that magnetic field, that magnetic field collaspes into the coil, creating an intense spark. that spark is then sent to the dist ad down to a spark plug. it must do this rapidly to be able to provide a spark for each cylinder at x-amount of RPMs.. the igntition module on electronic systems controls the speed of the power to the coil. pre-electronic systems, a point (or basically a switch) did this contant on-off power to the coil. there was a "bump" for everey cylinder on a small rotating cam inside the distributor. these bumps would kick off the point, turning off the coil and creating the spark. each bump was aligned with a cylinder.
anyway enough lefture, 6V at the coil during cranking is normal. due to the consant fluctuation of 0-12V.. and whats in between 0 and 12V? 6V.. Digital Voltmeters read the average voltage when theres a constant fluctuation. if you were to try an analog meter, you might be able to notice the flickering.