Alternator overcharging

Recently replaced the alternator on my 70 340 Dart. The new one has a smaller pulley and now I'm getting 17.3 volts at fast idle. Could pulley size be causing this? I've checked the wiring, and have repaired/ replaced some of it myself. I've got .1 ohm resistance in the charging circuit, which to me is pretty good. I've also checked for voltage drop with the engine off, which was also negligible. Maybe need a new regulator? Everything is grounded very well.