Either the 6 or 7 Series is recommended. The 6 series has an internal, dumb, regulator
that you can switch on if the external regulator
Note that both of these alternators are small case units and are not heavy duty. I would highly recommend using the optional alternator
(assuming that you have a alternator
regulator that can accept this signal) that will protect the alternator. In the case of the Balmar MC 612 and MC614, this protection kicks in should alternator temperature go above 220F.