hmm maybe scotchbrite on the sealing surfaces, and then use a dremel to port & polish the 1.9 MLS won't mean a perfect seal if its warped though...
i think those cracks look pretty bad i wouldn't personally use that head, i know you wanna be cheap, but if you were given that head u could always buy a new one off eBay and swap the valve train over, yeah that's 300 dollars but that head looks like hell and a new one will surely bring less headaches. i don't think the pitting would keep it from running fine but the cracks could i definitely get that head pressure tested if i had planned to use it. honestly I've never seen cracks as bad as cylinders one and two. looks like someone needed new injectors or had a ***ty pump tho.
X2 on having it pressure tested. Also tip it up so the ports are facing up and pour some form of solvent in the ports. WD-40 would work even. Then check to see if it leaks out onto the combustion faces. I'm most curious whether or not the exhaust valves on the first two cylinders are leaking. I have a theory bounding around in my head that leaking exhaust valves on a boosted engine can cause engine melting temps without registering high EGTs on a gauge and could cause that type of erosion without any damage to the other two cylinders.Andrew
I wouldn't even consider putting an old head on an engine without pressure testing it, making sure it's flat and at least hand lapping the valves and putting new valve seals on it assuming the guides are good also. VW heads are usually not on an engine for a reason so don't put yourself through a lot of aggravation by not getting it checked and by all means do use the studs like you said.
Hand lapping is accomplished by placing a small amount of valve grinding compound between the valve and seat and using a suction cup tool to rotate the valve in the compound. It basically works similar to sandpaper and helps the valves to seal completely.Andrew
I would also be a little concerned about the erosion next to the precombustion cup on that first cylinder - looks like it might affect it, maybe not.