I need to replace the gas tank in my '91 Civic and need to know whether I have a 1.5 or 1.6 liter engine. The tag on the underside of the hood says Honda Civic 1500 and the "Engine Family Identification" # is MHN1.5V5F1F3. Does that mean it is a 1.5 Liter Engine?

Yes, you have a 1.5L engine.