1965 Dart Alternator ground

It may be dis-information or it may be that for some time he had a 70/ newer isolated field (improperly called dual field) on there which has two insulated brushes, and so one must be grounded to work with the 69/ earlier regulator

The alternator is bolted securely to the block, both by the main mounting bolt,and by the tensioner, and the battery must be "main" grounded to the block in order to crank the starter. You will not get much more "grounded" than that!!