[bobH]

For the 'leave-it-alone' folks... It was about 14 years ago that I had my 59A apart for a valve job, and a couple other repairs. I found one of the 'part-number' cracks, #6, from in the port, across the deck, and starting on the cyl wall. Who knows how long it had been there. It never gave any problems that I was aware of. I agonized over repairing it for awhile, and in the end, just put the engine back together without doing anything to it. So, it's been that way for at least 14+ years, and maybe much longer. The engine is not doing anything bad - no overheating, does not use coolant (can run couple years without adding coolant), doesn't smoke, doesn't use oil, etc.
What more could I ask for? My point - maybe I've been lucky - don't know. But, in this case, doing nothing is working ok.