I just did this Sunday, but my van is not a synchro.  I hope this will help.
I'm a very novice mechanic and it was no problem--only took one trip to the
home depot ( I tried the local hardware but they didn't have metric!!)

On mine, the upper bolt took an 8mm allen wrench. I used a long 8mm allen
wrench with a handle to get more torque (I bought a whole set and the handle
for $10).  I started from the bottom, but found it easier to reach from the
top.  I could fit my hands past the hoses without too much problem.  You
could also use a socket with the 8mm allen sticking out if it and a 6"
extension--I'm not sure how the whole ratchet end would fit.  That long bolt
has does have a nut & washer on the other end, which I didn't notice at first.

The lower bolt was a 15mm, but a socket won't fit.  You'll need an open-end
wrench.

good luck,

Doug Demarest
Minneapolis, MN
86 Vanagon "kombi"