I've done this swap to my LJ. I can run the headlights, the heater on high, the rear window defrost and front and back wipers. At idle, just over 14 volts.
Still at idle, with everything running,when my flex-a-lite fan kicks in, the lights dim for a split-second and my guage goes back up to just over 14 volts.
It is a definate improvement over the stock alternator, as I would show a voltage drop to 10 or 11 volts with the accessories running. This was before the electric fan, which I installed that at the same time as the alternator.