I just bought my first mustang, a 1979 hatchback, I want to order some parts but they want to know if it's a base model or something called a giah model. how can I tell which one I have?

 

Since none of you mustang experts could tell me the differnce between the base and giah sub models, I went to google and searched, and found out that the base is a 5.0 car and the giah is a four cylinder car. I thought you boys knew your stuff? This is my first mustang, thats why I joined this forum, to get help with my build.