New cam and heads for original 273?

Cam Terms explained, at a basic level, for the novice in order to help choose a cam. Once armed with this basic knowledge, choosing a cam is easy and. An be done without a fear of screwing up badly.

Duration:

The amount of time the valves are open. The larger the number, the longer they are open. The longer there open, the bigger the breath it will take in or out.
When the duration is increased, the power. And of the engine moves up in RPM.

Duration is measure in 2 ways. Advertised and at .050, in which is when the cam begins to open the valve. When the valve opens to .050 lift height off the seat, that measurement is taken. This makes the cam look smaller to a degree.

Choose you camshaft based on the operating RPM as described by the manufacturer first.
Your cruise RPM should be in the lower part to middle of the rated RPM band of the cam.
This RPM must have matching parts such as intake, compression, carb, stall converter, rear gear ratio and the cars weight.

Also note that what a cam does in a large engine will act more radical in a smaller engine.

Lift: the amount the cam lifts the valves in theory.
(due to worn, inaccurate valve train parts, the lift stated may not actually be the lift you get. Also In addition to the geometry, valve lash for non-Hyd. Cams, full lift may not be realized.)

Overlap: the amount of time both valves are open.

Centerline: the lower the number the more of a choppy idle you will have and the harder time you'll tuning it at idle. Most performance cams are set at 110 which will give you that muscle car chop.

There, your armed with some knowledge, now go open up a cam book and poke around.