is the engine in the car,
or on an engine stand ?

the later is much better as you can get gravity on your side, but
rotating the engine until the head you are working on is straight up.

got a Bentley book for the o-ring positions ?

there is an o-ring at the base of the barrel, and the other one, the
green I think ,goes in a groove at the top of the barrel.
I lube my green o-rings with Vaseline so they won't catch.

I just put a wxbr engine together and I used toyota goop instead of the
vw goop - it's got to be better.
if you wish to try this,
call a toyota dealer and say you want the sealant that is used when you
change the water pump on a 95 toyota pick-up with V-6 engine - they use
this instead of a gasket or o-ring.  Costs about 15 bucks a tube, and is
the best silicone type sealant I've found.
Been using it in various applications for about 8 months.

Also, I put it on BOTH SIDES of the Rubber Water Gaskets
contrary to what the book says.  So far so good on that engine.

I REFUSE to call them head gaskets.
HEAD GASKETS are laminations of metal, fiber, asbestos,
whatever, but those rubber things are just water gaskets,
and a joke, really.

The amount that the head pinches the rubber water gasket is
medium-critical.  Once I replaced a head and after a year the rubber
gasket pinched and leaked.
After much research a dealer tech told me you try the bare head on the
block and if the gap is ( I think he said )
less than 4 mm YOU TRY ANOTHER HEAD  ( ! ! ! ! ).

the idea of standardized parts is they all fit exactly the same, EXACTLY.
 Hello VW.
If you complain enough to VW America they will admit it is a poor desgn
and help with your costs, or at least they used to.

  good luck, just do very careful work,  scott