What is the difference function-wise between the older "A" alternator and the "B" alternator?

Can the "B" alternator go on a all stock 71 Charger with no problems?

Square backs usually had higher amperage output.

The change in the case was due to a new design of the components. Unless you have a rather unusual mounting arrangement the two alternators will interchange.

Awesome - good news for me! Thank you Feets!

You need an extra wire for the square back field also[it has 2 fields].That and if you have a point reg toss it and get the replacement that looks just like it but is solid state.

can't say on a BB, but on the sb, you need to add a longer swing arm.
the gm chrome one they sell for 10 bucks will work with a spacer.
ground the extra field and you should be gtg.

I would think your 71 would already have the "B" 2 field terminal alt system with blue and green field wires. Otherwise as said space it forwards or backwards till the pulleys line up & swing it out with a longer bracket/belt as needed & if you only have the 1 green field wire on your 71 then just ground either one of the alt field terminals to the nearby alt case & instead you can unground the brush/brush holder so it's now grounded to it's case mounting nub for a cleaner appearance & if you are purchasing one I'd ask for one for an 85 M body iirc, which is a 78 amper

Square back on my 65 BB and the bracket fits like it did with the OE alt.I run an old MP water pump with the odd bracket so Im not sure if that changes anything.Rocky