Lyle from Bob's Mechanical called me today.  He left a message on my phone asking me to call back in a tone that made me wonder whether a relative of mine had died!  Turns out, the news was worse;  Both of my heads had one crack each between two valves. You can see one of these cracks in the picture to the right. 

Fortunately, my $50 engine had 2 good heads, though these heads weren't ported nor did they have their valve guides machined, they did have better seats.  Best $50 I've spent so far!