1968 318 alternator suggestion

I purchased an alternator that the local auto parts store's website assured me would fit my car. Unfortunately it doesn't seem to....but it almost fits. Comparing it to the alternator I took out, it seems to have some extra features (circled) in the housing that rub up against the engine block and header.

I'd rather not keep buying alternators and finding out they don't fit. Anyone else run into this? Does anyone have any recommendations for an alternator that would fit?
Hopefully you still have the old one, it is often worth fixing.

What you purchased is a "Revised Squareback" as explained here: Identifying Chrysler Alternators (1960-1976)

Not only does it not fit as well, but they draw more field current than the earlier models.
"Field" is also explained in the thread linked above.
Field current is the electrons flowing through the voltage regulator and the rotor's windings.
Excessively high field current may damage the points (or electonic components) of a regulator not designed to handle such high currents.

There is no guarentee that any alternator has been rebuilt with the proper rotor, so the issue sometimes surfaces even with the correct appearing replacment. This why I wrote that its best to hang onto yours. Replacements are like a game of roullete that we sometimes have to play.

More important on your replacement is that the connections are functionally correct for your system. You need to inspect the field brushes and be sure that one has an insulated terminal and that the other has a connection to ground. The voltage regulator output must feed to the insulated terminal. That's also explained in the thread linked above.

If you want to also do a field current test, its not difficult, just astep beyond some people's comfort zone.