Looking for some more power in my firebird?

its a 305 auto everything stock, i just switched the stock spark plugs with some bosche and wires with msd but im in need of more power i was thinking of a new carb would that effect my power? i was thinking a 650cfm or higher is that smart? if i want a 750cfm what do i need to do? thanks, also im not taking engine out i dont want to replace cam shaft