I just got through with the same exercise with my totaled '85.
You can find comparable vehicles on Autotrader.com and in your local
paper.  Find ALL the receipts for all the work, parts, accessories, etc.
for your Westy.  This made a very big difference in my case. (Only had
6500 miles on the engine, new tires, etc.)  This is important: ASK TO
SEE THE BASIS FOR THEIR APPRAISAL!!! In my case, they were getting their
information from a national appraisal service and all their sales data
was based on Vanagons but NOT Westfalias!! They were trying to make an
adjustment for a stove and refrig.  When I pointed this out to the
adjuster, they agreed to go back and review the whole thing.  Two days
later they called with an offer that I jumped at, above what I had
figured I would have to settle for.  BTW, find out what the 'salvage
value' is on your Westy.  Would you believe I bought mine back from the
insurance company for $407.00 ? This gives you the opportunity to part
it out for more than you paid them for it (depending on how bad it was
'totaled').