cam selection

I am an un experaced owner of a 350 small block i would like to put a cam in it but have no idea what the max lift i can go up to on my heads is. they are 305 heads that came stock with the motor for more low end torque i guess. can some one tell me the max lift i can put to my heads is and suggest a good cam for street use.

what am i looking at as far as the effected rpm i dont want to run a big stall in the trans so i can run it on the street ?