318 HP Estimate (Yes I know....)

I'm going to say 270HP

I'm basing this on the fact that a stock 2bbl 318 over here in Australia was 230hp and responded REALLY well to a 4bbl swap.

some headers would be your next step and would possibly get you around 285hp or there abouts.

Well I doubt I'll ever go headers since they came be a real pain for maintenance. My co-workers are all into HP while I'm more interested in torque.