This is not necessarily a comprehensive how to article, but more just a bit of a guide for a fairly simple process.
First up either make a gasket to fit on the head from scratch out of cardboard or gasket material (required if you have ported heads or street eliminators or the like that require gaskets that aren't off the shelf). If this is required trim the card to the exact shape of the inlet port.
In my case I used a standard type IV inlet manifold - it was slightly oversize in comparison the ports which was taken into consideration when match porting.
Using a tungsten carbide cutting bit in a die grinder enables you to take off material quite quickly (so go slowly!). I found some WD40/RP7 helped to stop the aluminium clogging up the cutting bit. I found a bit with rounded end helped to avoid cutting in any steps/edges into the manifolds.
Find a perfectly flat piece of glass (not all glass is perfectly straight by the way). If you ever see a scrapped photocopier - its glass is perfect! Then using sandpaper (I started with 240, then used some 400 to smooth out any scratches) steadily rub the manifold across the surface until the dye/marker is gone (but don't go too nuts and take too much material off).
Even though these manifolds were new, I thought I'd check. Used manifolds subject to heat and overzealous manifold nut tightening would benefit greatly from this process.
Because the amount of material I needed to take was relatively minimal, I only blended the manifold ports up to around 1-1.5 inches. If more porting was required on the manifolds, you would probably have to blend them higher up. For extreme applications, I've seen guys have to cut the manifolds in half to do the porting, then have them rewelded.
