The old school, simple port matching advice was to 'paint' the flanges with dykem or a lot of Sharpie, align the gasket on the flange and secure it in place. Then lightly run a scribe around each opening using just enough pressure to scratch the dykem/sharpie and not deeply score the flange. Then carefully open up the ports to the scribe line and blend back into the port roughly 3/4" to 1 inch. "Blend" is the operative word, air doesn't like sudden changes in direction.
Then came the whole "Anti-Reversion" (AR) thought/method/"technology". This said to open the downstream port (head if intake, manifold/header if exhaust) to the gasket opening, but leave the upstream port a little smaller than the gasket opening. How much ? Who knows, I've seen numbers vary so widely that I'll guess at least some had to have shorts moved aside to grab them. If you know what I mean....
I kinda buy into the AR thing and I kinda don't. On the intakes I'd be inclined to bring everything to the gasket except for the floor of the intake manifold. Leave it above the scribe line by roughly 3/32" The point of this is to cause a little turbulence there in case of liquid fuel flowing down the port floor. Would like to toss it back up into suspension because it will burn better that way. Does this work? No idea, but it seems logical & like it should.....
