My vote is for a homemeade welder. Ive been looking at building one myself I just havent gotten around to it. IIRC you want a ford alt because the regulator is external. I cant remember much more of the details though
Really doesn't matter too much. Even if you have an internal regulated alt, you are only a couple of case screws away from removing it.
Gotta tear it apart anyways, to remove the diodes.
Many late models are "externally" regulated by the pcm and have 2-3x the amps of the old ones.
Something like a nippondenso 160amp alt from a durango will really get you cooking.
Most alts will put out more than rated, but limited by case temperatures affecting the diodes. By removing the diodes and mounting them (new high voltage rated) remote to a big fat heat sink, amp capacity goes up as well.
The trickiest part is figuring out what you want to use as a rheostat/voltage controller on the field winding side. Obviously you don't want a full 12 volts "full fielded" for any extended length of time. Some have used dimmer switches or a variety of pedal controls.