first save your money by not upgrading to a 9" rear untill you need it, and likely you wont untill you get over the 400hp mark with slicks. a 3.55 gear is a good one to use for a decent compromise between street drivability, and performance, just remember though that at 65 you will be turning better than 3k rpm so fuel economy will suffer somewhat, and noise levels will be higher. you can alieviate that by swaping an o/d trans at the same time. as for the carb, the 600 is too big for a stock 302, in fact again untill you get over the 400hp mark you dont need more than 500cfm airflow. that said however you can make the 600 cfm carb work if that is all you have or are planning future upgrades.