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In my experience, the single biggest snafu made by first time builders is choosing a cam that is too large for the rest of the combo.

The key is coordinating the intake valve closing point with the available static compression ratio. If you have a stock 350 Chevy that has a SCR of 8.5:1 and you install a cam that is meant for a motor with SCR of 11.0:1, the intake valve will close so late in the cycle that you won't build sufficient cylinder pressure to make good power. The late closing of the valve allows the piston to push some of the mixture that has just been drawn into the cylinder, back up the intake tract to confuse the venturi and cause a rough idle. This is called reversion. It contributes to insufficient power at low rpm's and results in insufficient manifold vacuum to operate accessories such as power brakes.

Dynamic compression ratio takes into account the rod length and intake closing point. Paying attention to DCR will result in the optimum cam/scr combination to make maximum cylinder pressure for the available fuel used.

I've been playing with my dyno software and can tell you that I have found that no matter the internal components used, the power can be choked off at the inlet and outlet points on the motor. I simulated a 350 with stock-type intake manifold and 1 1/2" headers. Changing to a Performer RPM manifold and 1 3/4" headers pickup up 55 ft/lbs of torque and 90 hp!!!!!!!

Another snafu is choosing heads that are too big for the cubic inches and rpm range of the motor. Ultimately, the cfm rating of the ports is the deciding factor. For instance, the L31 Vortecs (12558062 casting) look too small for a 355 at 170cc intake runner size. But when you look at the flow rating on the heads, they outflow anything made previously by Chevrolet, including the double hump F.I. heads that are so sought after by newbies who really don't know any better. You can source 'em from a boneyard off of '96 to '99 Chevy trucks (5700 Vortec motor). Look for a sawtooth design on the end of the heads. When looking for aftermarket heads for a street motor, a good rule of thumb is the cubic inches of your motor times 1/2 for the intake runner volume.

As was stated by others here, it's a balancing act to get everything working together toward a common goal based on available fuel and what you expect the combination to do.