I picked this up from another site and and saved it. It might be of help:
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F355 alternator rebuild update, with part numbers. 10/13/2006
I have successfully improved the F355 Nippondenso alternator. It would have taken one day, but I was sent on a wild goose chase by a defective-out-of-the-box regulator.
The parts to buy are:
A regulator, brand name Regitar, part number VRH2005-4A
A rectifier (optional), which needs a minor mod, Regitar RN-02
The only place I found that sells them online is
http://www.holcombedirect.com/browse.cfm/2,55.html
The defective part I bought was a Transpo IN220, and during my visit to the alternator dyno, they told me that they had occasional trouble with Transpo (assembled in Costa Rica) and had the best results with Regitar (says made in USA on the box fwiw)
Dyno of totally stock alternator was 13.6 volts at 139 amps for 5 minutes.
Dyno of improved alternator was 14.1 volts at 161 amps for 5 minutes.
The gains are more from the regulator than the rectifier, we tested both.
The goal however is increased reliability. The VRH2005-4A regulator has some features that the stock one does not have in terms of circuitry to prevent shorts or failure when confronted by a battery, belt or wiring problem. The RN-02 rectifier, which is where the diodes turn AC into DC, is very heavy duty. The new rectifier is all copper instead of steel, welded diodes instead of soldered, thicker mount for the battery stud. The 6mm battery stud from the new regulator needs to be replaced with the 8mm stud from the original rectifier. This is reversible for future concours, where the rectifier part numbers must be original.
I also replaced all the tiny cheesy screws with allen bolts, which made life much easier. They are all 4mm x 0.7 pitch, and I needed 3 for the regulator 5mm long, 4 for the diodes 5mm long, and 2 for the regulator case at 20mm long. The local hardware store didn't have 5mm allens, so I shortened some 10mm ones on a sander.
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