As to the question of whether to repair the FI or replace it with a carb:
I was in the same position a few years ago with a '78 bus.  What I'd
recommend is making a good effort to determine what your problem is (by
reading Muir and the Bosch books) and then price what you suspect are the
bad components.  There aren't many VW junkyards around here, so when I was
going through this, I didn't consider used equipment.  You mentioned you've
already replaced the fuel pump so you've got some money in the FI system so
that would be a point in favor of keeping it.  OTOH, parts are pretty steep
for FI, and there's no guarantee you've got the culprit.  In my case, I
ended up going to a 2bbl progressive Weber for about $200.  I don't argue
that fuel atomization, etc. is more efficient with FI, but the nice thing
about a carb is that all your fuel delivery system is contained in one little
"box", rather than spread out here and there over your engine compartment.
It makes troubleshooting much simpler.  I'm not knocking FI, it's just that
it's kind of complicated and pricey so keep that in mind.  If you go to a
carb, you'll need a low pressure fuel pump, about $20 I think for an electric
one.

Pat Walsh, '71 Westy, walshp@ippdsgi3.nawc-ad-indy.navy.mil