charging system blues

TrailBeast said
You ... want a squareback

True. For a non-restoration, these generally perform better at low rpm compared to a similarly round-back with the same rating.

TrailBeast said
There are two alternators, a roundback and a squareback.

There two styles of alternator housing from the 1960s through the 70s. A point of clarification because this

TrailBeast said
You have..a squareback

is only true if a later alternator was installed.

The squareback was introduced in 1972.
http://www.hamtramck-historical.com/images/serviceHighlights/1972/1972 sh p24.jpg &
http://www.hamtramck-historical.com/images/serviceHighlights/1972/1972 sh p25.jpg

All 1971 cars originally came with an isolated field round back alternator.
These were introduced across the 1970 product line. http://www.hamtramck-historical.com/images/serviceHighlights/70 sh 71.jpg
These are mostly of interest to someone restoring a '70 or '71, especially if it has the correct casting number and date on both halves.

A pulley swap is relatively easy. Most traditional parts stores will do that for you.