I have one in my 84.  With a diesel 5 speed trans.  Mine came from a 92
Cabriolet and has the digifant II.  I didn't do the conversion myself, but I
have been all through much of the system and it looks like it was very
simple..especially compared to what I have been reading over on the Subi/Van
list and what those guys have problems with.  The 1.8l  I-4 looks to be
almost "plug-N-play", though as Robert mentioned, there is a bit of cutting
involved to make the intake fit...very minor..
  I don't agree about the diesel 5sp trans being too low geared..Mine seems
just right.  I especially like the low gear, which I use only when starting
on very steep hills or to crawl down very rough tracks..
  I cruise mine at about 70-75mph all day with no problems..I have been
driving the crap out of mine now for over a year, put about (a guesstimate)
20K hard and fast miles on it at that general pace with no problems..getting
about 23mph average.  The "mouse-motor" little I-4 is a very good choice for
my type of driving..
  It is not gonna be any kinda huge performance jump from a good WBX gas
motor..But certainly a huge improvement over the diesel Vanagon motor.  The
characteristics are quite different from what you usually think of for a
vanagon...It (the inline 4) likes rpms..Mine, for instance, wants to be
downshifted at 70mph back to 4th gear in order to deal with any terrain
change...You can, if you want, just floor it and leave it in 5th without
losing too much speed on a hill, but if you go back (down?) to 4th, you can
actually accelerate up the hill to about 75 or 80 before you think of
shifting..Takes a bit of change in your driving habits to drive it
'properly' (my 'properly')  Mine has a standard exhaust manifold running
into a big Magnaflo muffler and a very mild street camshaft change ($125 and
a couple of hour work) so it does add some ooomph at higher rpms..The rest
of the stuff is almost all VW standard..with a bit of  irrigation sprinkler
pipe fabricated to bring air in from the standard Vanagon air box..
  Very easy to work on also, with plenty of room under there, the oil and
water are checkable from the usual place..and I've been quoted $300 only for
a replacement motor with low miles..should I need one ever..
  Don Hanson