350 to 383 engine additional performance

Hi, I am not that familiar with carborated engines my question is basically what can i do to the engine to increase its power output. Its a 1975 firebird

Also a side issue not sure if it goes along with this part of the forum but, how involved or expensive would it be to change it from a automatic to a manuel or should i even from driving standerds or is it just not worth it to change it over? thx