You should be able to use your existing generator (if it is like the three brush ones I am familiar with). It will still have just a field terminal and a battery terminal. You can wire it up to a 3 pole regulator just like any 2 brush generator.
What you may want to do is adjust the third brush so that the generator can deliver maximum output. The 3 pole regulator will now take care of limiting the current.
The third brush is on a slide that will rotate its position around the commutator. Depending upon position of the third brush, the generator will produce more or less current. With the original 2 pole cutout, if you do a lot of highway driving, you set it for less current so you don't overcharge the battery. If you do a lot of stop and go, you set it for hight current to keep the battery charged.
You might want to take this opportunity to do an R&R on the generator, replace bushing, bearings and brushes.
I would not toss the original generator and regulator if you do decide to replace them both. The next owner may find extra value in having those parts.
Kurt
