Help me please tryin to beef up 318

Hey please feel free to say anything you'd like I'm new to this type of stuff okay so this is what I've got going I've got a 1973 dart swinger with a 318 in it the motor was rebuilt 3-5 years ago I want to beef it up so I've bought a Holley 650cfm 4bbl carb an eldelbrock performance intake and a set of 1973-1974 360 heads and I'm in the process of buying new headers and a cam so my question is what do I need to do to the heads? I've heard they need to be milled but how much what other work needs to be done before I do that please leave me any information you have this car is my little hot rod my great grandpa gave me before he passed and I'm a senior in high school now and I want all the motor work finished by prom this in April 2016