Sorry to hear about all your issues. I'm currently in the middle of my Aerovee build and am learning about all of this stuff as I go. I will definitely reccomend to you the following book, which is also suggested by Sonex in the Aerovee manual. It will do a good job of answering many of your questions.
http://www.amazon.com/Rebuild-Volkswage ... 0895862255One thing I'm curious about... when I was putting my crankshaft and camshaft into the case, I noticed some very close tolerances between the connecting rods and the camshaft. Given the amount of fore/aft play you had in your crankshaft, is there any evidence of connecting rods contacting any part of the camshaft?
Regarding your possible crack between valves, the above book recommends grinding away material until evidence of the crack is gone (i.e. remove the stress riser.) Within reason, this will keep the head serviceable.