I have an 84 that originally had a 305, but now has the same year 350, that was installed before I bought it. None of the emissions stuff is there (o2, EGR, etc.). Vacuum is high and it runs good, but it goes through a tank of gas faster than an alcoholic goes through a bottle of tequila. I noticed the distributor has a 4-prong ECM connector and a vacuum diaphram, but I always thought it was supposed to be one or the other. If I disconnect the ECM, it won't start. If I disconnect the vacuum, it runs fine at all speeds. Haven't checked the mileage without the vacuum yet. Has anyone else seen anything like this? Does anyone with an 84 have either one or the other or both? Is it possible that I was getting too much advance? Timing is about 8 deg., don't know the advance curve yet.