Building a high HP 383. About 1/2 track and 1/2 street, but not a daily driver. Trying to choose a distributor (going with CD), and trying to decide if I should just go with Mech advance only....from what I've read, it sounds like the vacuum advance is only going to come in at idle, and very low rpm cruising. Don't expect to have much vacuum. Any experience on this issue to share?