Barry, Thanks!!
From the '74 parts book, it looked like the65 Amp alternators may have had functional difference.
Now looking at the '73 parts book, I'm only more puzzled as to whether the part number changes reflect a functional or appearence change.

3438 804 is a single pulley 41 amp alternator assembly.
Parts books shows that housing as p/n 3438 711

The alternator on my bench, although unfortunately blasted by a rebuilder has the same casting number on the housing. Date is obliterated.

But I found some photos on-line of another 41 amp alternator that shows in both the '73 and '74 parts book. Red tagged 3755404 eBay item number: 142665980358
Parts book shows different p/n for both front and rear housings.
Casting numbers are the same!
Here's what I see different externally.
Front (Drive end) housing
Recess for hex head of assembly screw in the mounting ear.
Unfortunately not enough of a view of the back to see what might be different.