440 power gains/ aluminum head advantages?

At idle or part throttle the vacuum advance will be activated. Won't hurt a thing at part throttle as it's not under load. But don't forget, you're going to have to limit the total mechanical advance to around 34 degrees (without the vacuum can hooked up) to keep spark knock at bay. So you're going to have to either weld the slots up in the distributor and refile them to a specific length to give the proper advance, OR run one of the FBO limiter plates. There have been a lot of people complaining on a very recent thread about those plates advancing too much, including myself. That's why I recommend choosing a total advance and welding and refiling the slots.
okay sounds good. now i've got my t bar slots welded in most the way and i used a drill bit the same size as the advance weight posts to make it fit. but i can file them bigger if i need more advance. i'll play with the timing some more tomorrow and see if i can't get it happier. thanks for enlightening me about the vac advance function. i always find something more to learn!