Did you even open the distributor to see if the internal coil was even inside the distributor. If you didnt then you wont know if it was modified for the msd. Just open up the cap and check it out. If its indeed modify for the external coil setup with the msd then all you have to do is hook up the 2 wires leading to the place of the coil from your msd igntion box. ONce you have done this let us know how it turns out