There is a great write-up of how-to-do for just this project already available:

  http://www.oldvolkshome.com/19to21.htm

  This is the guide I am using right now, to get things set up for my engine swap in the spring.

dylan friedman <insyncro@YAHOO.COM> wrote:
  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