Heavy Duty Alternator
If its the big 100amp type, I would buy a volt meter, and do the amp gauge bypass as shown at
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
use a 6 or 8 ga wire for the alternator to the starter relay.
The old alternators that look like your original type really just SUCK. your headlights will dim at idle. just plain junk. The 100amp type is a delco design and is a much better design and doesn't have these issues.