If I remember right, I don't need a voltage regulator since it is built in to the alternator on the six motor. Is that right? Do I need a different relay board?

The internally regulated alternator did not come out until around 1980 with the 3.0L engine. I could be wrong. Porsche issued an update to put internally regulated alternators on older engines.

Since you are building a 2.0 as I remember, you will have an externally regulated alternator unless the PO changed it. The relay board is not needed as you can plug the external regulator into the 3 prong connector directly from the /6 engine harness.

The relay board does provide connectivity to the main harness for oil warning, alternator charge and a few other things, but that can be worked around by matching function of the /4 main harness wires to the function of the /6 engine harness wires.

I did use a relay board (/4) on my first conversion. I also used a /4 engine harness and matched function of the wires to the /6 engine harness.

Oh and one problem identified with the internal regulator alternator was that under high heat engine loads the alternator warning light would come on. The regulator sits very close to the case and gets overheated. An alternator warning light on a /6 engine is also an indication you have lost your fan belt and have no engine cooling.

Can you recommend an external regulator?

The Bosch one is the easiest and should plug right in. The factory ones actually were adjustable, so a good electrical shop should be able to adjust it if needed. Trying to find one these days may be a problem, however.

BTW, the voltage regulator plugs into the relay board and is held in place with two screws. If needed, the regulator can also be simply plugged into the wiring harness if you want to get rid of the relay board.

You should have a Bosch 55 AMP alternator on your 2.0 as I remember. Use your Bosch VR from the /4.