Etek, you might also want to check the point resistance, which is how well the points 'ground' the coil. With the points closed, you should have very little resistance (less than 1-2 ohms) from the terminal on the distributor to the engine block. If this connection is not good, then the coil will not be able to build enough voltage to create a good spark and the excessive resistance could alter the spark's timing.
The distributor on my 51 has an external vacuum advance, that is, the vacuum advance can is stationary with the distributor base and turns the top of the distributor externally. There should be a small braided wire that connects the moving (rotating) part with the stationary base, providing a ground path. In more modern distributors, this small braided wire is under the base plate for the points
