After fighting over heating problems for a long time I finally thinking about replaced the mechanical advance only distributor with one that also has both vacuum / mechanical advance. I understand the engine temp could drop as much as 20 degrees at least in around town driving with that type of distributor. Now I'm really confused about what of HEI distributor i need. My Nova has a 350 engine, 750 cfm slayer carb. The Comp Magnum cam i have gives me only around 9-12 inch's of vacuum at IDLE. So what vacuum advance unit do i need to run with that low of engine vacuum. Summit has lots of distributors but i don't see and spec. on the vacuum unit on them. I understand their are a lot of different vacuum unit made for different engine vacuum conditions.