my experience with sticky rear drums is that prolonged bashing with
a rubber hammer will get them off. If they are turning okay, then they
are proabably rusted to the spindle (the thing that holds the lug studs)

I usually lose patience with the rubber hammer and use  a 2 lb. hammer,
protecting the drum with a sacrificial piece of 2X4 lumber as I bash
away, Liberally pump in Liquid Wrench (Not WD-40) around the
lug studs and give it 10 minutes to work its magic.

IF you want a sure fire solution - assemble tools, remove 46mm wheel
nut, go inside wheel and remove outer CV joint cap screws (you need
either a 6 pt or 12 pt cap screw bit - check yours first)

Protect the end of the CV with a baggie and drop it out of the way of the
wheel. Now pop the stub axle through the wheel and remove. Now you can
bash on the drum and shear the rust side-to-side as opposed to trying to
shear it by extension.

if you pumped in a lot of oil then you will need new shoes (probably
why you are int there anyway) - also if you wire brush the surface of the 
spindle and apply a thin (very sparingly) coat of high temp grease on the
spindle then next time the drums will slip off by hand like mine :-)

if you do go for the "sure-fire" method once you have the CV half
off wont you want to clean and repack your CV joints since you werent
doing anything this weekend anyway?????

My 83 Vanagon (a little more difficult than Bus because the CVs are deeply
recessed into the axle housings) took me about 4 hours to do all four 
CV joints. 

have fun and stay clean!