The 2G IAR was the very very very last Ford alternator to use a 6203. The 3,4,6 G NEVER used a 6203. The 6303 is an absolute certainty.
Even the larger (before the 3G series) 70-90-100 amp large frame uses a 6203 but never ever ever the 6303 in the earlier alternators
After a few thousand 3,4,6 G remans I sorta know this stuff.
And one last thing all the alternators use color coding on the regulators. Do not substitute a different color regulator or mighty interesting things will happen to a digital dashboard.