'81 was a bad year for horsepower for all engines. The key to getting more power from any engine is the same. You have to ''follow through'' whatever you do. Air and fuel are mixed and enter the engine. They go through the valves into the combustion chamber.There they are compressed and burned. On the exhaust stroke the piston forces the burned fuel mix through another set of valves. It exits via the exhaust manifold, then through the exhaust piping and out your tailpipe.
So to ''follow through'' you try to improve the entire trip of the fuel mix. An example would be: 2 four barrel double pumper holly carbs sitting on an edelbrock ram air intake manifold (increasing the first part of the trip). A set of polished and ported heads (increasing the flow through the valves). A Crane race cam at this point would further boost the flow (increasing the amount and the time or duration the valve stays open). The exiting gases will have no problem leaving the heads (you already polished and ported them). Now the gases flow much faster through a set of 2'' Hooker Headers (the first and most important part of your exhaust). Complete the trip with low restriction Thrush mufflers through at least 2 1/2 inch piping.
You can see that you have only improved the exit portion and while you should have gained some power, there is plenty more to be had. Most guys on a budget will just improve the entrace and exit, and neglect at least going for a ''race'' or ''street ground'' cam.