How certain are you that a "bottle" is a pint bottle?
Six egg yolks is rather high for just 4 cups of cream. That also begs the question of how large were the eggs likely to have been? I use 4 extra-large eggs in 6 cups cream, but I'm guessing eggs at that time were likely much smaller than today's.
The sugar and vanilla amounts would be more appropriate for the smaller amount of cream. So maybe those eggs were on the small side.
One of the beautiful things about ice cream is that the precision of the recipe doesn't matter too much. Cold sweet cream is always good! Add vanilla and it's sublime.