Let me preface this by saying that I am only repeating what I was 
told, and cannot verify its accuracy. I will also add that I am not 
a GEX supporter, having had both a GEX engine and transaxle fail 
almost immediately upon installation. I had to fight VERY hard to 
get the problem resolved.(Detailed previously on the Vanagon list.)

Another engine rebuilder that I deal with once told me that they 
would periodically order GEX heads to use on their motors when they 
were backlogged and could not rebuild their own on time.  Because 
of their concern for QC (particularly because they were warrantying 
a product that they did not rebuild themselves), they would check 
out the GEX heads one by one before installation.  Said that they 
discovered that, despite GEX's claim to use oversized valve seats, 
a large percentage of the heads they inspected had not even had the 
seats replaced. After they called GEX to the carpet on this, the 
instances of this nature decreased (but did not go away).  The 
company said they still use GEX heads in a pinch, but continue to 
find that they must inspect every single one because GEX's QC 
standards are not as stringent as their own.

Ron Salmon