I've heard that Liquid Wrench doesn't ignite/burn/ smoke as badly as the others when used intermittently with a torch to alternately heat up, then apply penetrant oil to the parts.  I concur with tapping the parts with a hammer, but also add that using a box wrench or T-handle with socket to alternate loosening and tightening to let the debris inside the threads loosen up without jamming the fastener.
  Also, I used anti-seize (sparingly) on the studs (after removal from the heads) and nuts.  I use this on practically every exposed thread on the vehicle for future ease of maintenance.  Either the next owner, or myself will appreciate this small step.
 I double-nutted the studs out and chased the threads with a tap.  I do have some Stahlwille stud-removers, but they can indent the threads badly, if a lot of force is necessary, where double-nutting won't hurt them at all.  
 One of my exhaust studs was stripped out at the head, so I drilled and tapped for a step-stud (I don't have helicoils).  This one was hard to get at, so I used my right-angle drill adapter (from Home Depot) to assist me in this tigh area, so i wouldn't have to lower or remove the engine to get at it.
  I also ground the ends of the tabs off the lower pushrod cover tins to allow easier removal/ installation later.  

Hope this helps,

Mike B.

  ----- Original Message ----- 
  From: Ken Wilford 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Saturday, May 16, 2009 10:26 AM
  Subject: Re: Advice needed for replacing front and rear header pipes and hardware

  What I have found is that many times it looks worse than it is.  I only
  use 6 point sockets.  If the original size (13mm) seems loose don't try
  it and strip it out, go to the next size down (12mm) even if you have to
  pound it on.  Use a torch!  You can pick up a map gas torch at Advance
  Auto or Autozone or Home Depot for not much money.  Be careful with it
  but heating up the head in the area right around the bolt will work
  miracles in releasing the seize they have taken.  Of course use your
  choice of WD-40 or PB Blaster on the hardware as well.  I have had very
  good luck with this method and haven't had to drill/tap for a while this
  way.  Take your time, put studs and copper clad locking nuts back in on
  all the exhaust ports.  That way you can cut the nuts off with a chisel
  the next time.  We sell the S&S Header exhaust system for $349 which
  many folks buy and have good luck with.  It is about a third of the cost
  of the stock system at the moments and is good quality, made in the USA
  as well.  Let me know if we can help you further.

  Ken Wilford
  John 3:16
  www.vanagain.com

  Jeff Hartman wrote:
  > Hi, The bolts (I think they are hex head cap screws and not studs with
  > nuts) that attach my front and rear header pipes on my 86 - 2.1
  > vanagon to the engine look very corroded.  It is time to replace that
  > portion of my exhaust system.  Is there an archive perhaps even with
  > pictures and instructions of what I am going to need to do to remove
  > the hardware, and replace it with something that is easier to get out
  > next time?  I understand this is going to be long, knuckle crushing
  > process, because my local repair shop really does not want to touch
  > it.  The pipes are still intact, but I have been avoiding this like
  > the plague. I could use a very dumbed-down description if anyone can
  > help me with that.
  >
  > Thanks, Jeff Hartman
  > Juneau, Alaska
  >
  > 1986 Vanagon 2.1 L
  >
  >