I have a tool that I found in1989 for removing the huge nut keeping the rear
drums in place on my 69 Westy.  It was a chunk of steel with cutouts for a
1/2" breaker bar and the large nut.  The idea is to apply force to the
breaker bar while at the same time striking the flanged end of the tool with
large mallet.  This worked well for removing the nut but you need to strike
very hard to start the loosening process.
Installation is the reverse - just strike the flange until the nut bearly
moves and then keep striking until you line up the next slot with the axle
hole.

I believe the tool came in 42mm for earlier vans and 38mm for the later vans
with detachable drums.  The only reason to remove the nut on later models is
if you have to replace the stub axle bearings.