318 rpm drops to 400 in gear WHY???

distributor feeding mechanical advance in at idle, because its 1200rpm, and when it pulls into gear that mechanical disappears when idle speed drops. Possible?

Need to sort out the timing first before worrying about anything else. It will likely need at least 18* initial is my guess. Setting total timing is an absolute waste of time at this point.

484 cams need lots of convertor and initial timing. They aren't particularly friendly in smaller LA engines.

Vacuum leaks?