On your distributor with points, the idle timing will be where you set it initially. As the rpm's advance, so does the vacuum to the distributor. With an HEI, you will have the timing advanced with a source at idle. Thus, the reason for ported for points, manifold for HEI. As you sit right now, put it to the "timed" port. when you change it over to HEI, change the vacuum source.