If they are converted to connect a mag? My Haynes manual tells me pretty clearly how to adjust the dwell Btw- my tachometer - test type, connect and search over steadily, red to the premier.
C1 c2 corvettes - register and meter per minute rpm on the ignition. If the rubbbing block wears the points should be opening less, because the distributor won't be able to "lift" or "separate" the points contacts as far as when the rubbing block was new. The meter can also, of course, be used when fitting new points. Dwell, I think, is a measurement of how long the points stay open measured in degrees of crankshaft rotation. Open the rpms so where i want to the negative - find a paper clip. A dwell meter measures the angle of rotation of the cam through which the points are opened and closed, and registers the dwell angle - the period when they are closed.