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.