What is the process to head space a virgin AK barrel?

cut the extractor cut, push barrel into the trunnion after   checking  trunnion and barrel size, .001-.0005 interference fit. push in and check with  HS go and nogo gauge. Drill barrel pin 7mm.

http://home.comcast.net/~restoreit1/

Kinda what he said^^^^

The extractor cut is a factor with some new barrels but can be done with a die grinder or dremel.

I take a rough measurement and seat my barrel "deep". I put the barrel in a freezer and slightly heat the trunnion. This allows me to have a "slip" fit. The barrel falls into the trunnion with no pressing (until the temparatures become equal).

Now it's in the trunnion a little deeper than it should be, it's easier to press it out than in, you won't bend it by pressing out like you can by pressing in. I start pressing it out a little bit. Depending on how close you are, you may just put a little tension on the press and tap the top (where the ram is, "helping" it go down) with a hammer to "creep" it out. Keep checking with your headspace gauges until you are there.

I use a .250" end mill to make a flat surface to drill. Then drill slightly undersize and ream to provide a press fit for the pin.

The trunnion is pretty hard and will usually act as a guide to keep the drill straight if you don't have a mill/endmill. Make sure it is tight in the drill press and that it is true/parallel to the chuck. I don't recommend milling with a drill press because they're not intended to take the side load and can cause injury or damage if the chuck comes out but, a straight down plunging cut with an endmill should not be a problem.

I use a mill and ream but you can do it with a drill press and number or letter size bit. I can't recall the size offhand though.

should be  a tight close on a go gauge.