What seems more important about the 1.8 liter head is it fits into a
vanagon without raising up the engine lid somehow.  I looked at a bunch of 4
banger VW motors sitting around in my local junkyard..The owner of the VW
specialty yard pointed out the two types of  small motors. The 2.0 liter has
the whole intake on the right hand side of the head, while the 1.8 liter
head has the intake and the exhaust on the left side...  When you stick one
of these little guys into a van, it lays over, with the right side up..So,
if you have the 2 liter head with the intake up, it is too dang tall to fit
properly...hence, people put in the1.8 head with the intake that actually
fits...I understand the heads are interchangable..somehow..So, if my motor
ever blows up, I guess I will find a 2 liter block and stick my head on
that...
  If you are looking for a lot more power, rather than just a better all
round motor,  a normally aspirated 2 liter motor that doesn't fit properly
seems like a kinda silly way to get not much more power...Why not a turbo, a
supercharger or a Subaru motor, if power is your goal?
  I will be running my little "mouse motor" soon on a friend's dyno...It
will be interesting to see how it actually turns that drum, compared to all
the other options available for pushing a van..With just the simple tweeking
of a better cam and exhaust, it makes my van able to pass all the stock WBX
ones I go by on hills, and I don't have any dependability issues so far..
  Don Hanson