It's a piece of cake.
I did it 100 % to 86 specs,
Including the cooling system layout, which is different - the hoses above
the transaxle area, and water distribution box there.  All that.
I put the ecu under the back seat etc.
BUT ..............tell you what I'd try now if I had time to do it, is run
the 2.1 on the 1.9 fuel system to try that out .  Here's why :
I have  an 83 westy that the PO claims is a 2.1 block, but it's all 1.9 spec
in every other way. It does seem to run quite strongly. It sure runs more
strongly than the 2.1 I put in my 85 Wolfsburg Weekender - tho that is an
auto trans, and they sure suck up power and throttle response,
And ...........the most powerful stock factory engine is a 2.1 that runs a
1.9 type fuel system, with no cat ( and maybe no oxygen sensor ) that I read
about. Forget the engine code. Supposed to be 110hp I think.  For markets
like Finland. 
But yep, it all goes together. 
You won't have a dynamic oil pressure circuit for the dash, so the oil
pressure switch by the crank pulley, you'll just ignore that. 
And if you can keep all 1.9 cooling system on it ( which isn't quite as good
a  cooling system I don't think as the 2.1 ) that will simply the swap.  To
do it 2.1 like, you need about ten or  2.1 cooling system parts, from an 86.

But the basic answer is, there's no big terrible gotcha about the
electrical/electronic interface. You 'might' have to get think a bit about
interfacing the instrument cluster and engine, but nothing really jumps to
mind right now, other than that minor oil pressure switch thing. 
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
dylan friedman
Sent: Sunday, December 09, 2007 9:16 AM
To: vanagon@GERRY.VANAGON.COM
Subject: 2.1wbx into 85 GL

I am contemplating swapping in a fresh 2.1 wbx in place of a failed 1.9 in a
85 GL.
I have numerous late model 2.1 engine bay harnesses and ecus.
Is this a plug and play type swap or is the older wiring from the ignition
and front of van not capable of the swap?

TIA,

dylan