Pros: Much greater charging capacity at low engine RPMs (e.g. long, slow descent at night with throttle pulled back and all radios, lights, instruments, and other electrical loads on), greater reliability, typically higher output current rating than generator.

Cons: If battery is completely flat and there isn't enough voltage to energize the alternator field, even if you hand prop to get your engine started, the alternator won't charge your battery, so you'll be without radios, lights, and other electrical accessories. If you have a dead battery, it's best to remove it and bench charge it if you have an alternator.

The Jasco alternator conversion kit is about $750 from <http://www.aircraftspruce.com/catalog/eppages/jascoaltkit.php>. Count on about six to eight hours labor. 

You're welcome. I replaced the DC generator with a Skytronics Jasco alternator conversion kit in my 172D four years ago, and it's been totally reliable. I'd do it again in a heartbeat.

There are good reasons why all the automobile and airplane manufacturers changed from generators to alternators in the mid- to late-sixties.

We upgraded our tired old Delco generator on the O-300 to a Lightweight alternator (dynamo) STC using the 6.1 pound lightweight B & C unit (STC by Endowment Enterprises 480-650-0883.  It produces 30 amps, and requires no battery voltage to charge and regulate since it is self-excited.   After a load analysis on the airplane we found that we only needed about 20 Amps, so this was a great lightweight choice for our 172.   We have a friend with a C-150 (O-200) who is also looking to do it.    The kit comes complete with all switches, wiring, circuit breakers, gaskets, warning lights and detailed instructions.  Great upgrade- supposed to be 2000 hours between service intervals, and uses the standard Continental drive gears from the Old generator / alternator.