assuming the engine has stock compression you should hit 300RWHP...The thing is the E-cam for some reason makes good power on a dyno but it may not perform like the numbers suggest on the street...However, with AFR's you would benefit more from a cam that had slightly more aggressive duration and more lift...A good cam with AFR's can mean 20RWHP increase...
The flow numbers on the exhaust side are the same...however on the intake side I believe the 185 flow about 20-30cfm more than the 165...HOWEVER, the 165 are better on a 302/306 motors due to the fact that they are a smaller chambered head and will make power in the lower RPM's because of it...Now you can also put 185 on a 302/306 but you will need to go with a steeper gear to make up for the velocity with a bigger chambered head...Both heads are excellent but with the 185's you have to notch the stock pistons in order to avoid piston to valve clearance...To get the most out of your setup...have your lower Cobra intake ported and get a custom cam...with just those two changes you will make a huge improvement in your car's overall performance...