I see a few problems with your plan. First off, Impala SS’s are VERY heavy cars. Around 4000lbs. You’ll be running a full second off the pace from the get-go compared to and f-body. Second, you want to do all the bolt-ons first with internals, and then put the boost to it. What will happen is this…with a turbo you’ll have to buy new headers (again) and replace pistons (again). Basically you’ll build it for the bolt-ons and then have to re-build it for the boost. You should only buy parts once for your car. Think long term whenever possible UNLESS your budget is of no concern. Make sure the first bolt-ons that you get, are compatible with your long term boosted plan. If you are going turbo, I wouldn’t even bother buying headers for the car, what would be the point?