It actually will work (I tested this theory a couple of years ago).  However
the 2.1l Airbox won't fit because of the hoses in the engine compartment (it
kinda squishes up against them and I was not comfortable running this way).  
I then adapted the 1.9l airbox, but this is not as easy it is seems.  I had
to cut that plastic housing and then fabricate my own gasket out of gasket
material.  You also have to replace your 1.9l Intake Air hose (that accordian
looking hose between the AFM and the throttle body) with the 2.1l hose since
the AFM outlet is bigger for the 2.1l.  It worked very well when I was done
however and I have these Air Flow Meters (2.1l) for $120 new (not rebuilt- no
core).  The rebuilt AFMs are a crap shoot from my experience and from what
customers have experienced.  Sometimes they are great, sometimes they are
just as messed up as the AFMs you took out (temp I is still bad, etc).  Hope
this helps.

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242