[OrrieG]

Both my HEIs (stock GM units) have have vacuum from the carb port to advance the mechanicsm. The engine will start and idle but since the dist is not advancing the timing driving will be a chore. It needs to come from the carb fitting for the dist, it is designed to read the correct vaccum for the dist. Other fittings on the carb, base and manifold are just use to capture vacuum for the wipers, auto trans and brake booster. If you are running an auto, vacuum is need to determine shift points, brakes will work without a booster but I would not risk wrecking my truck. Don't know of any vacuum ports on the block, can't image where they would pull from.