Hi Gerard,
   so the short story is what blows up your engine is high peak pressures.
That is worst when the flame front moves at just the right speed to be about
complete when the piston reaches top dead center.   You can delay that point
of peak pressure by either running a little lean or very (150 dF or more)
rich of peak.   When you do that you are spreading the pressure curve over
more degrees of crank travel.   Power is the area under the curve.   So you
get almost as much pressure with way less peak pressure.
   All the bad things about leaning happen on the rich side of peak.  If
you can get past 50 dF lean of peak, it's all good.  but as Scott said, it
is really difficult to get there with a carbureted engine.   If you are
stuck with ROP, at high power settings you are going to have to get your
first to peak cylinder way over on the rich side.
   There's lots more interesting detail about this which you can learn from
the APS seminar which is now online. here:
http://www.advancedpilot.com/store.html

   It is really good stuff. I went thinking I would learn about LOP but I
really learned a lot of other stuff about my engine, how easy it is to
destroy it, and some things I would change if I were doing a new engine
installation.  If you are curious you will find it well worth the money and
time.

   If you are cheap, you can see John Deakin's articles at avweb.  They are
also good but not as comprehensive.  Go to the following page and find
Pelican's Perch articles #63 through #67.
http://www.avweb.com/news/pelican/182146-1.html

   All that said, there were some bad years for valves, guides, and seats.

Colyn