If you have a 'high-rise' intake, would that cause no need for a carb spacer? And do carb spacers really increase performance? And, what is the difference between dual and single planes? Thanks.

a dual plane intake is split into 2 parts..1/2 the carb flows to 4 cylinders..and the other 1/2 to the other 4...a single plane has a direct shot to the intake ports...carb spacers are engine specific..no 2 types of engines will respond the same to spacers...one engine may see an increase..while another seamingly exact engine will see a decrease...4 hole spacers are said to help low end torque while open spacers help higher in the rpm range..a spacer "fools" the carb into thinking its bigger

Bigjimzlll gave a good explination.
I'll add a little more info since it seems you may be a little new in this department.

A dual plane intake also makes the carb you are using seem smaller to the engine.

At this point in time the high rise dual plane intakes are the best thing to run on a street motor.

Dart Kool Can
Edelbrock RPM Air Gap
Brodix HV 1016
World Products Sportsman II
Weiand Stealth
Holley Street Dominater 300-36
Edelbrock Performer RPM

All of these are good dual plane intakes for small blocks.Cams with an intake duration of 216-244 at .050 will work well with them.

If your cams intake duration is smaller than 216 at .050 you should have a regular Performer,or a Weiand Action plus.

If your cams intake duration at .050 is larger than 244 you should be runing a single plane intake such as a;

Edelbrock Victor JR.
Edelbrock Super Victor
World Products Motown
GM Bowtie