help with "hard root beer" recipe

I am planning a hard root beer for my next batch. I started with Charlie Papazian's MacJack root beer recipe which suggest 2 oz sassafras bark and 2 oz sarsparilla for a 5 gallon batch. However, in doing some research, the 2 oz called for seems more in line with a one gallon batch, unless the recipe is calling for actual sassafras root instead of sassafras bark?

I am basing this mostly on recipes from SACRED AND HERBAL HEALING BEERS and also the book Homemade Root Beer, Soda, and Pop (also see root beer reference here:

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So now I am wondering if I should make some adjustments to the MacJack recipe, and if the 2 oz was for a 1 gallon batch and not a 5 gallon batch what about the other ingredients called for in the recipe, such as 1 vanilla bean?

Anyone else who has any experience brewing hard root beer or even soft root beer --- please advise!!!

Thanks