My Maternal Grandfather was born in Portugal but then moved to lourenco Marques(now Maputo), then moved to South Africa and hence became a SA citizen, He is now deceased and so is my Mom is it possible and if so how do I go about applying for a Portuguese passport, so far the only document I have is my Grandfathers SA identity.

Your grandfather's original nationality and birth has nothing to do with you being able to get a Portuguese passport. However, if you mother was born in any Portuguese province you would be able to obtain a Portuguese passport.