318 2bbl carb to 4bbl carb Need help

I have a 1969 Barracuda with a 318. The 2 barrell carb it has is not working too well and am wanting to replace it with a 4 barrell carb. What would I need to do in order to make this conversion? Would I need to get a new intake manifold as well? If I need to get a new intake manifold what else would I need to do?