The VanAlert app and it's list of Vanagon repair shops is good. Here's another list:
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Also, IIRC, the OP wanted references to shops that do work on Subaru conversions. I live in the Sana Cruz area, so if you find yourself in my digs, there are 2 shops that I can recommend:
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Vivid Vans
http://www.vividvans.com/
831 201 4894
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* Good for all things Westy and Suby!
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Rick's Auto Shop
(831) 475-2470
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* Good for all things Suby engine related.
SoquelDude