Not sure what type of booster you are using. The old "HydroVac' unit I got had an external inline check valve "to install a minimum of eight inches above the vacuum inlet" to prevent back siphoning of oily gasses into the cannister. Most modern boosters I've seen have a check valve mounted right to the front of them, where you slip the hose onto the fitting.
From what I understand most boosters operate with about 9" of vacuum. Your relatively healthy motor should be producing 16"-21". IMHO you'll be just fine.
