The heads may have air ports drilled right under the bottom of the port. Some lock tight on Allen studs to block them off so they don’t leak exhaust might have to be done. This depends on the year of the vehicle. It is pretty much a simple job. The worst thing that might have to be done is to use a tap to clear up the threads in the head. If you don’t have threads there, I’ve seen tin foil used though most like something like a JB Weld or other epoxy.
A little bump in the distributor time can help as well. Do you have a 2 or 4 bbl carb?
