Fellow vanagon types 
I assemble on average 2 WBX engines a week and I don't have problems with ripping water jacket seals. I will explain my method.
1 ) I wire brush and debur the block then I grind out any pitting with my drummer tool and fill it with epoxy and file it flat. Masking tape is useful to hold the epoxy in place until it cures. This job is not so easy to do in the van but I still think its needs to be done to create a surface that is not sharp and flat 
2 ) I lay in a small bead of black silicone in the channel of the water jacket gasket. The reason for this is not so much for sealing as it is for lubrication of the gasket. I also lay in a small bead on top of the gasket to help lube seal.
3 ) With one nut I bring the head down against the gaskets and I repeatedly wiggle the head as I do this to unload any preloading on the water jacket gasket. Keep in mind the push rod tubes twist the head in a way that can rip the gasket as the head is tightened down 

Bob Donalds 
http://www.bostonengine.com
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