Long story short.Heads and cam won't show a huge jump with out the carb but the carb won't show a huge gain without a better exhaust.You have to move more air IN and OUT to get a huge gain.But doing the heads and cam is fine but adding the 4bbl and headers will show up better.Keep in mind the pistons are a big HP killer in the 318.If you put the 2bbl back on try not to over jet it as you want the A?F ratio to be right more than just throwing jets at it.