Your alternator will run full bore for a few hours charging
that bank, possibly resulting in the alternator cooking
itself. External regulators (such as the Balmar
MC-614) with their temperature sensing prevents this as it will derate the alternator when it heats up.
I'd be willing to bet that MaineSail (linked in the post above) would say that an external regulator is required for any alternator charging
a large AMG bank.
But hey, your 60 amp replacement hasn't melted down yet... Maybe it will any day now or may you never deeply discharge your bank, so the alternator never works hard.