Volvo Repair: head gasket, volvo 850 glt, backyard mechanic

Question
I am wanting to buy a 95 Volvo 850 GLT Wagon that has been driven hot and now has water in the oil.  The seller says its a head gasket.  

What would you say percentagewise that the head is warped/cracked?

Is it a difficult job for a backyard mechanic to change the headgasket on this particular vehicle?

Thanks!

Answer
  Serenity, How hot did he get it and for how long? Odds are the head is warped at minimum. Price a used/reconditioned one before deciding to proceed. Odds are you'll be doing a valve job too. How long did he run it with the coolant in the oil? These deals are risky at best. If someone said you can have it if you get it out of my yard, I'd go for it and at least tear the head off and see what I had???
   Difficult for a backyard mech. But not impossible. You are supposed to have special tools to hold the cams etc., but I've seen some pretty ingenious backyard solutions for a one time job. VBG

Mark