Re HB Chris-- yes, the pulleys are different as well, from what I interpret. The e3 has the same pulley as e9 according to the part numbers. 12311277561
However! Yes, however, I found an alternator which came from 75-76 3.0is, and it appears to have internal regulator. But more importantly, the pulley looks different that the e9 pulley, contrary to the pulley part number which is also 12311277561.
Additionally, the 3.0is alternator also has a different part number, 0-120-489-606, whereas the e9 has part number 0-120-489-609.
See below pictures of alternators and pulleys.
1st 2 pictures are of e9. The last 4 of 75-76 3.0is.