Exhaust change. How bad will it be?

In short. no. I dont think the calibrations, or even the amount of calibrations a stock carb gives you will be enough to make this even worth thinking about. Get another engine if you want stock looks. I would suggest a large small block..416/408, and a cam chosen to run with factory manifolding. The long stroke will keep things very usable, even more sneaky, but you'll have much more usable power on tap.