what des it take to stroke a 360 to 408?

ok so im stuck on what to do with the cam situation. i would like to run the highest amount of lift that i can get away with, but im not sure what that is. .477 lift is for the xe268h and then the xe284h has a .507 lift. does this sound about right if my head are ported and i have the heavy duty springs? is there anything else required to run that much lift? The guy that built my motor is telling me i need to replace the timing chain when i do the cam swap. the one in there has less than 5000 miles on it. Is this true?