Typical green coolant didn't magically turn evil overnight, Honda blocks from the 70's to today are made of virtually the same grade aluminum. Seeing how unusual it is for water pumps to leak any significant amount as-is, it's not important.

It is perfectly fine to mix in store bought coolant. Properly mixed and changed at the recommended interval, you will see no problems. Honda passenger cars have lived with "evil" green coolant without ill effects since the 70's.