Bill,
OK, now you've got my interest!  A crank mounted alternator could make a
great backup power source.  So, why can't we come up with a simple
method of mounting a PM alternator, or 55 amp ND, on the end of the
crankshaft?  That shouldn't be too hard to do. (easy for me to say) I went with the Aero-Electric Z-14 approach (two alts, two batteries).
I rationalize that chances are slim that both alts will quit on the same
flight, unless I break a belt and it takes out the second belt.  If I
lose both alternators, then reserve battery power (dual Odyssey 680's)
will be used to get me to a safe landing site.  The plan is to replace
the belts at every annual.  Biggest worry is engine overheating &
seizing due to loss of water pump.  An EWP would fix that.  Mark I believe they have also done crankshaft pulley alternators.
Bill Jepson