MSD race units like the early 404 and the 7 race boxes of all types require a coil that has a lot different windings inside the coil, I don't remember exactly if the stock coils are 400 to 1 and the MSD coil need 200 to 1 or vice a versa
I like the early Mallory #28880 or the same coil with the MSD sticker on them The later small red MSD coil for their race boxes work well also