An isolated ground alternator can not be used with the ground controlling regulator (although some rebuilders hack them).
See
Identifying Chrysler Alternators (1960-1976)
The squareback is easier to service yourself, and more likely to produce more power at lower rpm.
With a parts store or aftermarket alternator there is no way to know for sure what the output potential is.
The revised squareback is heavier, draws more field current, and is clocked differently which can put a strain on the wiring.
Those might be the test specs at 1250 rpm.
By Chrysler's rating method, in 1966 they were 30, 37, 46, 60 amp.
see TSB 66-78 page 2
https://www.hamtramck-historical.com/images/TSBs/1966/66-78_page2.jpg
A-bodies did not normally get a "60 amp".
View attachment 1715856596
Chrysler's in vehicle service test was usually done at 1250 engine rpm, at 15 V.
That's the only real output number that I'm aware of.
For example a "30 amp" can produce 26 amps at 1250 rpm and 15 Volts.
View attachment 1715856607
Nobody reveals what rpm or voltage alternator amp 'ratings' actually are based on, and there is no industry standard. Probably something close to maximum, and rounded off as convenient.
A bigger list here for 1970 Dodge trucks with the new isolated field alternators
The 1970 Hamtramck Registry - 1970 Dodge Truck Service Highlights Slideshow (Chapter 4)
Yep!
I've seen that Cardone and others rebuilders make that rating the common offering.
By Chrysler's naming/rating 34, 41 and 50 amp were generally supplied.
View attachment 1715856595
I'd take an original '50 amp' Chrysler alternator any day over a 'remanufactured' '60 amp'
if given such a choice.
Generally there is little choice for every day users.