It's possible, but the heads you most likely have would require some porting, and some work...

The main problem with the late 70's 400's was they dropped the compression ratio's and the power went right along with that drop. So for the most part, the heads are the key ingredient, to making the power. (the best way to do it)

Think of the engine as a big air pump. The more air you can get into the engine, and the more air you can get out, will produce more torque and HP.

So, depending on what motor it is (code?) and what heads you do have... you can do all the basic bolt on things (Headers/Intake/Carb/Ignition etc... and gain some power, enough to feel... but with out doing some upgrades or even changing the heads, it may not be enough... but will be a change in the right direction.

You may need to tell us more about the engine before you get some more specific answers?

Engine year and code. Any mods now like headers, carb, intake etc.. What car is it in, what tranny, what gears in the rear etc... All variables that will effect the final outcome.

Good luck, keep us posted -
Brett - 67 Drop Top 455!