I have worked on older marine diesels that used gears to drive the OHC.
 I think they never took off in autos as they are probably very noisey. The
Marine diesels made such a racket you never noticed the gear noise.
    The SVX intake cam is gear driven off the exhaust cam instead of having
another loop in the timing belt.  The intake gear is very interesting and
complicated. The gear is actually two gears, sandwiched together.  The two
gears have a spring which pushes both sets of sprockets away from each
other, to eliminate lash, and probably noise.
     I used to think timing belts were cheesy.  After a decade and a half of
use in the majority of cars, I am over it.  My only dislike of them is what
OEM dealers charge to change them.  Many are a ripoff, and some cars they
are difficult to get to. Timing belts are cheap, smooth, and very quiet.
     All that being said, having a belt versus a chain had no effect on our
choice of the ECOTEC over the ZETEC. I do think it has a slight economic
advantage for us and a long term customer, but not enough to tip the balance
one way or the other.
  I am working on putting a 2.4 Ecotec (177 hp)in my Westy right now.  I
can't wait to see how it compares to the other engines that have been in the
same van over the last couple of years. (SVX, 5 2.5's, 1 2.2).  I can't wait
to get the adapter plate and flywheel done so I can bolt it up.

    John
    East Coast Vanagon