The alternator which enables the easiest conversion is the Delco internally regulated type 10-SI. These were used on most GM cars from the mid 70s through the mid 80s. Any decent parts store should either stock them or be able to order one on short notice. They are also readily available online.
Detailed instructions for the conversion are available here:
This page is also worth looking at, because it explains about the clock position of the plug-in connector and will be of help when you run into a clueless partsperson:
If you need additional info please post again.