joy is right life cycle assessment is difficult to do but its still a thing
in my opinion that the amateur can play with and do almost as well as the
researchers ;).  its really all about what metrics you choose in your
analysis and how YOU weight the inter change between metrics in your
model.  coming from an industrial background and having an "environmental
sense" i often find that alot of the real "scientists" that i see play
with life cycle analysis are pretty clueless about what it takes to make
an industrial product and the practical aspects of how that product will be
used by the masses.

the best people i have seen to make a good stab at this are engineers that
worked in their field then went back to school to get a phd in some type
of environmental field.  a one person interdisciplinary approach i guess.
then when they come out with a seemingly practical model they get heckled
from both sides the policy flakes and the engineering at all costs people.

to take this back towards vanagon content lets talk engine conversions.
this doesn't come up much but was part of the attraction for me to do my
engine conversion.  if you convert to most engines newer than the wasser
boxer you will gain better emissions by rule of thumb.  also on the long
term life cycle analysis bit if you select a engine that has a longer
interval between rebuilds there is less "rebuilding" energy spend per
engine life cycle.  as a side note many of us lament "throw away vehicles"
but if you sit down and think about it as long as those vehicles are
recycled and emissions go down over time that is a good way to ensure new
cleaner technology adoption.

jonathan