Converting automotive alternator to put out 48V?

I figured that maybe some of the regulars in the generator forum could advise on this. Apparently (if you're an electronics whiz) it's fairly easy to get an automotive alternator to put out as much as 120VDC by modifying the voltage regulator. This could be very useful for charging large banks (48V, etc...) of batteries via an alternator coupled to a small engine. Has anyone seen a good FAQ out there of how to do this? I just don't know enough about resistors, diodes, etc...to make sense of it all without pictures or very detailed step by step instructions.