Be Careful. The port size should Remain the same or DECREASE the closer it gets to the Valve. This is all the way from the plenum to the valve. If the Ports size increases, air speed will slow at some point, reducing torque and therefore power. If you open up the intake port too much, even if you port match the intake manifold, to the point where its size is greater that the opening of the intake manifold, you will get a power loss.
so in effect - measure the port size you want to open it up too. Measure the port size at the start of the intake runner. Make sure it is Bigger in the runner than at the head. Only then will you see benefits.
More air is good, but slowing the airflow down is very bad. There have been instances where people port matchinig manifold to head have recorded power losses. You have to be careful before starting - and very careful with your measurements. triple checking is par for the course.
That being said - if Planned Plenum runner area (cross sectional) > Planned head port area then its not too hard to do.
First get an intake manifold gasket to use as a template. Mount in place on the head. Mark out the maximum area allowed by the gasket for the port. Do the same for the Manifold. using a carbide tipped tool in a die grinder, grind away the metal between the outer edge of your mark and the open ports. feather it into the body of the runner, both in the head and into the port. Smooth out casting dags. Do not remove any material from around the valve stem support or from the back of the valve in the head. Feel free to smooth out rough spots though. You want the area at the back of the vave to be as small as possible to promote faster air flow.
Do the same with the intake manifold , but here you can remove metal to make the runner volume larger. Ideally, the entire path, from valve back to the mouth of the plenum, will gently taper out, increasing volume as you go.
port matching simply makes the Port in the head and in the manifold exactly the same in size and shape. Least interruptions to airflow that way, as well as least turbulence induced by odd shappes in the path. Do NOT polish the intake side. Polished runners/ports allow fuel to bead off on them, dropping fuel out of the air stream. This is bad. Leave them a little rough, or ideally, with a 'swirl' pattern in them.
Feel free to polish the exhaust side though. There should be stuff all unburnt fuel here (ideally) and the exhaust side is all about letting the hot gases vent as easily and smoothly as possible.
Again, remove dags, and port match if you can do so without creating any weirdness in air flow. Some people cut away the Valve guide into an arrowhead shape to maximise exhaust flow.