Putting 12 volts to a 6 volt coil is a guaranteed way to burn the points, as the coil is designed to work properly at 7.5 volts (charging system voltage with the engine running, against a fully charged 6V battery). A 12V GM coil operates properly at around 9.5-10 volts, and is designed to use a resistor to drop the charging system voltage (14.7 or so) to the lower voltage. During engine cranking on a 12V system, a bypass circuit allows the coil to run on straightr battery voltaqe. Simply swapping coils is not sufficient to make a 6V-12V conversion of the ignition system.
A dwell meter is nothing but a voltmeter with a specially calibrated meter movement. It is actually measuring an averqge of "points closed" voltage measured downstream of the coil (zero volts) and "points open" voltage which is the same as battery voltage. Changing the amount of time the points remain closed alters the apparent voltage the meter sees.
Around the time Chevy switched from a 6V to a 12V ignition system, they changed the profile of the distributor cam, and also changed the specification for the dwell setting. The point gqap also changed, from .016" to .019", which accounts for the difference in dwell. For instance, a 1954 standard transmission distributor, P/N 1112388 calls fpor 38-45 degrees of dwell. A 1955-56 distributor P/N 1112403 calls for 28-33 degrees. All of the rest of the 12V distributors call for the lower setting. The 1112403 distributor is specified for all 6 cylinder passenger cars through 1962 according to my Motr Magazine service manual. Truck distributors might have a dirfferent part number.
Jerry
