A couple of points of confusion... is the alternator single or dual field? I believe the original in a '68 was single field but it may have different now.

If single field, the inexpensive parts store replacement will be electronic inside and should work fine with electronic ignition as posted by Rocks. The original points style single field may not work well with electronic ignition.

If dual field, again the standard parts store replacement should work fine with electronic ignition. Its electronic inside like the original... just updated. This is what MOPAR used with electronic ignition. If you prefer the black one from Mancini, it should work fine also.

The "constant voltage race" dual field regulator will also work with electronic ignition. The drawback is a long run on a hot day may overcharge the battery... and initial charge after a cold start may be slower. Still many folks have been happy with this setup with no problems.

If it was mine, I'd just go to the autoparts store and purchase the electronic replacement regulator to match the alternator type. Cheap and effective.