Charging Battery with Alternator - Warning

It's really about controlling the charge rate, which is a function of battery size and charge state. Because none of these older systems regulate current to the battery.

The warning, and the point of this thread, is that something will get damaged. The only thing that varies is what will get damaged more.
If the alternator is running at or close to its maximum capacity for extended period of time, it will get damaged.
If the battery is drawing over 25 amps for extendentd period of time, connectors will get damaged. The ammeter connectors just being two of the several that will likely be damaged depending on the model.
If its wintertime in upper Michigan, the battery is probably frozen...and recharging a frozen battery will not end well.
If its in the middle of summer and a 'sealed' battery, a high charging rate could also do bad things to the battery.

When these cars got heavy duty 60 and 65 amp alternators, they also got matching heavy duty, higher capacity batteries.
I do not know the entire reasoning, but clearly in part the higher capacity battery uses up a smaller percentage of its stored power for any given operation.